Four reasons we don’t apply the 80/20 rule

Why can’t we make more use of the 80/20 rule? I’ll review what the 80/20 rule is, explain how it can be powerful, then give four reasons why we don’t take advantage of it.

What is the 80/20 rule?

The 80/20 rule is amazing when you first learn about it. It says that efforts and results are often very unevenly distributed. You’ll get 80% of your results from the first 20% of your efforts. For example, maybe your top 20% of customers will provide 80% of your profit. Or when you’re debugging software, often 80% of the bugs will be in 20% of the code. Once you become aware of it, you’ll see 80/20 examples everywhere.

There’s nothing magical about the numbers 80 and 20. The general principle applies if 93% of your results come from 22% of your efforts. The numbers don’t have to add to 100. The principle is just that outcomes are unevenly distributed, more unevenly distributed than you may think.

Applying the 80/20 rule

Applications of the 80/20 rule are everywhere. For example, if you want to learn a foreign language, you don’t buy a dictionary and start learning words from page 1 and work your way to the end. Some words are used far more often than others. You’ll be able to use a language much sooner if you learn the vocabulary roughly in descending order of frequency.

Software optimizations can be extreme examples of an 80/20 rule. Sometimes 98% percent of a program’s time is being spent executing just five lines of code.  Finding those five lines and tuning them is far more effective than randomly tweaking things here and there in hopes that the changes improve performance.

Why don’t we apply the 80/20 rule?

If the 80/20 rule is so powerful, why don’t we use it more often? Why don’t we concentrate our efforts where we’re likely to see the best results? Here are four reasons.

  1. We don’t look for 80/20 payoffs. We don’t see 80/20 rules because we don’t think to look for them.
  2. We’re not clear about criteria for success. You can’t concentrate your efforts on the 20% with the biggest returns until you’re clear on how you measure returns.
  3. We’re unclear how inputs relate to outputs. It may be hard to predict what the most productive activities will be.
  4. We enjoy less productive activities more than more productive ones. We concentrate on what’s fun rather than what’s effective.

If you address these issues in order, you might get stuck on the third one. It can be hard to know what is most productive. Our intuition in this area is usually wrong. For example, maybe the most effective thing to do is very simple, but we overlook it because we think the answer must be more complicated. Or maybe we confuse what we need to do with what we want to do. Collecting data is the best way to find out what really works. The results are often surprising.

Sometimes the world changes and we’re stuck doing what used to be most effective. For example, some of the most persistent ideas about the “right” way to develop software come from studies of done forty years ago. It’s not enough to collect data one time.

More on Pareto and power laws

9 thoughts on “Four reasons we don’t apply the 80/20 rule

  1. Well, the main thing is really that we don’t need to use it as often as we think. You see, 80% of the success of the rule results from 20% of its application.


  2. “LOL@Barry Leiba” — OR —
    “LOL” [applying the 80/20 rule to my message string]

    Yeah, the 80/20 rule IMO just begs for a beating with the “reductio ad absurdum” stick.

    I wrote a long essay about it but “80/20”-ed it into one sentence. The 80/20 rule is just like a screwdriver.

    Maybe I’m confusing “80/20”-ized language with laconicism. But isn’t that just like …

  3. Another way of putting the third reason we do not use the 80/20 rule more often is that it is descriptive not prescriptive. It’s easy to look back on your efforts and notice which 20% of inputs accounted for 80% of the outputs but not so easy ahead of time.

    There’s also probably an availability bias at play: you tend not to remember all the times the amount of effort was commensurate with the payoff as, well, it’s what you expect! When you get most of the payoff for what seems like only small amounts of effort you tend to remember it. Perhaps in the hope of learning from it and doing it again.

    It’s also interesting to note that if you were successful at predicting the 80/20 rule and only focussed your efforts on the crucial 20%, then it would eventually become the 80/100 rule. Much less appealing.

  4. “You’ll get 80% of your results from the first 20% of your efforts.”
    I am not sure, but is it that? From FIRST 20%? I think that is not true; not first efforts, because “the first” opposes to unevenly distribution of results which are expecting from the 80/20 rule –Although 80’s scale (successes) and 20’s scale (efforts) are completely different means, they seems that are complicated combined.
    In my view, this is a very general rule if we say “the crucial 20%”, we probably means 20% of efforts which are more recognizable as significant parts. Then if we concentrate on them, we will be more skilled till improve to 80/100 as Mark Reid mentioned above.

  5. I agree with Mark. The 80/20 rule is an observation. Which is observed succintly in Barry’s comment.

  6. So Jethro Bodine goes to business school, and comes back ready to make money. He gets $10,000 in singles from Mr. Drysdale’s bank and sets to sorting the bills by the cement pond. Uncle Jed comes in and asks him what he’s doing. He says he’s got a sure fire way to make a lot of money. In business school he learned about the 80/20 rule, so there are 2000 singles worth $8000, and he’s sorting them out. Jed says, “Well that’s fine, boy, but how are you going to make any money? The other 8000 singles are only worth $2000.” Jethro replies with a glint in his eye, “That’s easy, Uncle Jed – I’ll sell them to someone who doesn’t know about the 80/20 rule!”

  7. I used to think the 80/20 rule derived from the bell curve: just bend over to pick up ±1.5 σ and you’ve gathered 80% of the dollar bills.

    But some of the comments (eg, Reza’s) seem to also be referring to diminishing marginal returns. In that sense 80/20 might be suggesting that “it’s OK to not finish a job” as long as you have gotten a sufficient amount of the benefit from work. (Or, it’s OK not to finish your sodapop–if you’re on a diet and got 80% of the pleasure from a few bites.)

    The latter would seem to conflict with the superstar effect (Cal Newport, whom you’ve also quoted), wherein returns are magnified at the far positive extreme.

  8. “We don’t look for 80/20 payoffs.”

    Yeah, I think #1 is a lot of it. We need to develop the habit, at the start of any task, of asking what is the 20% that really needs to get done. Certainly a lot of routine tasks like email can go faster if we’re looking to get the crud out up front.

    On the other hand, it’s also very important to discern when 80% of the benefit comes from the LAST 20% of the effort. Building a spacecraft is like that, as is going to college, at least if you want to get a job.

    If we’re clear on which activities are like the latter, we may be less prone to perfectionism in the bulk of our work, where it pays to be less thorough, and even to allow a mistake from time to time.

  9. If anyone wants to know where the “rule”, that is not a rule but a ‘rule of thumb’ from the result of a power law distribution, comes from.

    I’d add that one should never ‘apply it’, but rather use it as an approximation or a heuristics from where a first level approximation can be made, properly followed by more rigorous analysis when a significant result is needed.

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