The vast majority of effects are produced by a small minor of causes. Economist Vilfredo Pareto first identified this in numeric terms in the 19th century: it seems that, in many diverse settings, the approximate numbers of 80 and 20 pop up. 20% of businesses produce 80% of economic growth. 20% of people own 80% of monetary wealth. 20% of the students (the most disruptive ones) take 80% of teachers' time in public schools. 20% of products sold by a company produce 80% of its revenues. And so on.

The fact that the numbers add up to 100 is a coincidence, and 80 and 20 are just approximate. A mapping of cause and effect in any situation may reveal that 72% of causes produce 23% of effects. The point is human intuition causes us to just assume that all our inputs produce an equal amount of outputs, but this is almost never true.

Most people know the 80/20 rule (also sometimes called Pareto's Law) either implicitly or explicitly. It is often mentioned in business literature, for example. After explanation of the principle (and introducing a type of graph designed to show cause-to-effect mappings) the book proceeds into application to business. It hammers home how important it is for businesses to focus on cutting out the 80% of causes which are getting them little gain, and boosting or increasing the 20% which get them the most gain. Fire your worst customers and put more resources into your best ones. Fire your underperforming or break-even employees and give the now-free funds and resources to your highest-performing ones. Discontinue your lowest-selling products and increase your inventory and marketing for your best-selling ones.

Employees are a particularly tough area, because when it comes to humans, we have a sense of fairness. Even though the best engineer or marketing rep or salesperson may produce 1000% times more output (and more profit for the company), they are rarely paid 10 times as much as their colleagues. Worse, in any reasonably-sized organization, there are a large number of people who are only break-even or perhaps even cost the company more money than it brings in. In this case the best choice is to fire them. It sounds harsh, but the author points out that everyone has their talent, and by keeping someone at a job that they are not a good match for is just as bad for them as it is for the company.

About halfway through the book shifts gears from business application to personal/life application. This is a rather sudden shift but I think it gets a lot more interesting after this. A lot of the text from here forward is a bit self-helpy, but it's good self-help. For example, it recommends writing out your top 20 happiest times in life ("happiness islands") as well as your 20 least happy. Look for patterns. Chances are you have gotten 80% of the happiness in your life from 20% of your time. Why not cut out activities, situations, and people who were not involved in your happiest times?

It stresses people's apparent powerlessness to change their circumstances. Yes, most of their time is not happy - because they have obligations. The author thinks, and I agree, that people have more power than they think. If family, friend, or work obligations are not truly enjoyable to you, then they probably aren't that effective for those that are seemingly placing the obligation on you. You do everyone a favor by cutting those things out. For example, one will only be successful in a line of work that one is passionate about, i.e. that one enjoys. So if you don't enjoy your work, then it is probably also a poor way for you to make money. Quit, and look for something that you are passionate about. It's probably out there, and chances are, you can make more money doing it.

One chapter covers mentorship. It points out the importance of having not only trusted business partners, i.e. peers, but also to find someone who can be a mentor to you (giving you their wisdom and experience), and also to mentor someone else. It may seem that the mentor doesn't get much out of this relationship, but in fact they get the invigorating excitement of a fresh perspective, and perhaps a window onto cutting-edge developments that are more visible to people not yet set in their ways in whatever field the mentor and mentored participate in.

My favorite chapter is 10: Time Revolution. It describes what I have always done without thinking about it, and which - according to the author - are the sort of habits that make the most effective people. He describes this approach to life as "smart but lazy." Too much hard work actually dampens your effectiveness, because you never have time to mull over what you've done and envision a better course of action. The protestant work ethic tells us that we should always be working hard, but his recommendation (which he feels leads naturally out of the 80/20 rule) is to work hard some of the time, and be lazy the rest of it. Be extremely selective about the things you choose to work on - that is, be both smart (choosing well) and lazy (limiting the number of your choices). He scoffs at "time management" - which is just a way to cram in more work without necessarily producing more output - as well as the term "free time." He recommends you think of all your time as just your time, and that you spend it as wisely as you can. You should have a good mix of work and play, and every single moment that you spend should be spent on something you enjoy and something that produces maximal effect. H points out that people who follow this approach to time tend to be seen as eccentric, because they do not spend their time in the same way as others. But this is exactly why they are so much more effective than others.