Most stories about the 80/20 rule start with Vilfredo Pareto, a truly international guy. He was an Italian economist but he was born in France and he studied the distribution of wealth in England. The story goes that he first got interested in the phenomenon when he noticed that 20% of the pea pods in his garden produced 80% of the peas. He later looked at land ownership and noticed that 82% of Italian land was owned by 20% of the people. Then he discovered that 80% of the wealth in England was controlled by 20% of the population. Around 1906 he published some of his findings and the 80/20 rule was born.[i]

 Other scholars took note such as Joseph Juran, a Romanian-born American engineer who was a pioneer in quality control on manufacturing lines in the 1940’s. He noted that 80% of problems are due to 20% of possible causes. He coined a phrase for this: “the vital few and the trivial many.” Specifically, he found that 80% of problems with products were caused by 20% of the production defects. By focusing on and reducing those 20% production defects, overall quality could be greatly increased at the least amount of expense. Juran became an important figure in Japan after lecturing there extensively on quality control issues. [ii]

 In later years, Juran changed his now-famous expression to “the vital few and the useful many” to remind us that the other 20% of the problems and the other 80% of the causes aren’t really just insignificant or trivial. Let’s remember that Pareto didn’t throw out the smallest 80% of the pods because they still gave him 20% of his peas. [iii]

 The 80/20 rule and the importance of not ignoring the 20% was popularized in a much-discussed book, The Long Tail: Why the Future of Business Is Selling Less of More  by Chris Anderson, 2008. The idea of the long tail in reference to book sales, for example, means that while a publisher has a small number of best-sellers with hundreds or thousands of copies going out the door every week, they also have hundreds or thousands of titles selling a few copies a week.

 Over time, many examples of the 80/20 rule have accumulated. If we go to the web we will quickly find all kinds of things. Be aware that I present these as “things you see on the web” with obviously varying degrees of validity. But here are some examples with my interpretations in some cases:

• The top 20% of buyers for almost any consumer product account for 80% of sales, according to Philip J. Cook’s book “Paying the Tab.” This is true for many if not most retail and consumer products.
• In general, 80% of usage is by 20% of users. Maybe this applies to the copy machine in your office. Let’s say 100 people work there but 20 people probably make 80% of the copies or use the machine 80% of the time when it’s being used. Maybe this applies to the coffee lounge as well. It’s probably true that 20% of people are drinking 80% of the coffee. Or that 80% of the time that someone is in there, it is one of the 20% of people who use the lounge most frequently. 
• 80% of revenue comes from 20% of customers. You’ll have to measure this for your own business. But it is true for many businesses. [JF1] 
• 80% of complaints come from 20% of customers. You probably know some of their names.  Here’s a related one: 80% of customer complaints arise from 20% of your products or services.[iv] 
• 80% of profit comes from 20% of the product range. Toyota makes at least 14 models: Corolla, Camry, Land Cruiser, Prius, Yaris, RAV4, 4Runner, Highlander, Mirai, Tacoma, Tundra, Avalon, Sierra and Sequoia. 20% of 14 models is 2.8, so let’s call it 3: We’d have to ask them, but does Toyota make 80% of its profit from 3 of these models? Probably so. And you can probably name them.
• 80% of sales will come from 20% of your salespeople. Let’s hope the 20% who are your best sales reps are getting a good enough commission that you will keep them. Otherwise your business is in trouble.  I’ve also seen this expressed as 20% of your workers produce 80% of the results.
• 80% of work absence is due to 20% of your staff. Maybe you can name some of these folks too. 
• 80% of road traffic accidents are caused by 20% of drivers. Indeed some people are more accident prone that others. This is why insurance companies increase your premium every time you have an accident. Are you one of them? Just kidding!
• 80% of a restaurant’s turnover comes from 20% of its menu. How often does someone order that toasted cheese sandwich featuring the brie with wild mushrooms? But like Juran would say, the infrequently ordered items aren’t insignificant. If you cut your 100-item menu down to the 20 items that are most often ordered, you will lose customers.

• 80% of your time spent on a website will be spent on 20% of that its pages. (The above 9 come from [v])
• And some more web examples: 20% of websites receive 80% of the traffic. You were probably on some of these sites today.
• 20% of your carpet or flooring will receive 80% of wear. Think of the paths where you walk from room to room.
• 20% of criminals are responsible for 80% of crimes.
• In the days of video tape rentals, at any given time, 20% of the titles were responsible for 80% of the rentals.
• The top 20% of wealthy individuals have around 82% of the world’s wealth. This hasn’t changed from what Pareto found in England more than 100 years ago.
• In the United States, 20% of the patients use 80% of the healthcare services. This is from an Atlantic Magazine story about a program focusing on having health care workers serve these 20% of people at home to make their hospital visits less frequent. In other medical news, 80% of STDs are transmitted by 20% of the population.[vi] In epidemics, 20% of people (‘super-spreaders’) cause 80% of the infections.
• The top 18% of words (ok, almost 20%) used in the English language are the words used 80% of the time. We’ll be looking at this in more detail.
• 80% of problems in computer programs come from 20% of the bugs.[vii]
• 20% of the features cause 80% of the usage [viii] Think about your TV remote control. How many buttons do you frequently use? How many buttons have you never used? (How many buttons are there that you don’t know what they do? Let’s be honest here!) 

So now you have a better idea of what the 80/20 rule is about.

Let’s stop for a minute before we go forward to let me introduce the idea of what I’ll be calling “hard and soft” 80/20 rules. You will see that once we move away from talking about things that can be quantified, such as sales, income, web site visits and buttons on a remote, we need to be aware that the 80/20 “rule” is more of a guideline than a rule. Similarly, when we later discuss power “laws,” of which the 80/20 rule is one, keep in mind these are seldom hard and fast “rules” or “laws” even though they are colloquially called that.

So when you read something like this: “80% of the problems in a relationship are caused by 20% of the issues,” you recognize immediately that you are never going to be able to quantify things like “relationships” and “issues.” I’ll call findings like these “soft rules” as opposed to quantifiable “hard rules” involving numbers that can be calculated. But even the hard rules may not be all that concrete; even Pareto found numbers close to 82%, not 80%. So even in analyzing hard rules always keep in mind that 80/20 may actually be 79/22 or 83/19. (We’ll also see later why those two numbers don’t have to add up to 100%.) 

Still, there’s a lot of value in the ideas these observations present as long as we are aware that some of these things make sense intuitively even if we can’t measure them scientifically. So let’s look at a few “soft rules” that we can find hanging out there on the web. I put my comments in parentheses after each one. Most of the following are from this site. [ix]

• If you are not producing the results you desire, change your strategy and refocus your energy on the 20% of activities that will produce most of the results. By eliminating or outsourcing trivial activities, you can free more of your time while accomplishing more. (Obviously it’s up to you to quantify “activity” and “results” to make this guideline useful to you.)
• 20% of financial decisions result in 80% financial results. Everyone’s budget is different, but most major expenses are from debt (credit cards, mortgage, student loans). By attacking prior debts and not acquiring new debt, you can improve your finances dramatically. (Depending on how closely you can quantify these measures for yourself you might be able to make this one into a hard rule rather that a soft one.) A related “hard” rule which you probably can calculate is that 80% of income is derived from 20% of sources.
• 20% of stressful activities produce 80% of the stress. Find the small portion of activities that produce the most stress and eliminate them. (This is probably quite true, but good luck trying to quantify this one.)
• 80% of the space on shelves hold clutter. (I personally know this one is true and I will define all that stuff as clutter until I get up to 80%! When I get rid of stuff I’ve found it helpful to think “I’m not throwing away those 10 T-shirts I never wear: I’m giving someone else a chance to wear them.”)

• 80% of luggage is excess, 20% is essential. (Six pairs of socks. Really? But how about that bottle of aspirin? It’s only essential if you need it. Let me know after the trip. This website author makes this suggestion about packing for a trip: If you think you might need it, leave it. If you can’t live without it, bring it.)
• You wear 20% of your clothes 80% of the time. (You know those favorite jeans and that sweater you love? This is one that you could quantify and examine as a hard rule for yourself. And we’ll be talking about this one in more detail shortly.)
• 20% of foods contribute to 80% of weight gain. (I let my friend have the last piece of pizza last night, so this morning, I’m taking the extra donut!)
• Losing weight is 80% about reducing what you eat and 20% about exercise. (A fancy filled donut may take up to two hours to burn off on a treadmill. I should have had the pizza.)
• 20% of relationships provide 80% of value. Focus on nurturing the small percentage  of relationships that provide the most value (spouse, family, close friends). Moments spent and memories made improve the quality of your relationships. (This one is a direct quote from the author of the website. I’ll leave it to you to try to quantify this one.)
• 80% of information is useless; 20% is crucial. (Unfortunately we often have to look through the entire 80% before we can determine the crucial 20%). [x]
• 80% of a teacher’s time is taken up by 20% of the students. [xi] (This may be a good thing or a bad thing.)

So you get the idea of what the 80/20 “rule” is all about. There are plenty more examples out there on the web and in books. Let’s take a look now at why the 80/20 rule exists and how we can show how it is derived.

[i] Mar, “13 Examples Of The Pareto Principle – Simplicable.”

[ii] “What Are Some Real-Life Examples of the 80-20 Rule (Pareto Principle) in Practice? | Investopedia.”

[iii] “Joseph M. Juran – Wikipedia, the Free Encyclopedia.”

[iv] Simon, “Pareto Principle (80/20 Rule).”

[v] “The Pareto Principle, or 80/20 Rule – History, Explanation and Examples, for Time Management, Change Management – Learning and Development and Business Education Materials.”

[vi] Simon, “Pareto Principle (80/20 Rule).”

[vii] [NOTE TO ME: The above 6 are from https://www.linkedin.com/pulse/website-traffic-zipfs-law-shane-parkins counting the last 2 above websites]

[viii] “Understanding The Pareto Principle (The 80/20 Rule) | BetterExplained.”

[ix] “Pareto’s Principle: The 80/20 Rule – Billy Shall.”

[x] “Microsoft’s CEO: 80-20 Rule Applies To Bugs, Not Just Features – Page: 1 | CRN.”

[xi] Simon, “Pareto Principle (80/20 Rule).”

 [JF1]Maybe add this to the consumer product two bullet points above. Seems very similar