Occasionally you read or hear an idea that sticks with you, that makes a big difference in what you think and how you act. Often the idea is obvious in hindsight. Some examples for me are the ideas of the law lord as a model of the law, the Necker cube as a model for storytelling from evidence and what lawyers do, and the following idea about persuasion.
The easiest way to persuade someone to do something is to show that it will get them something they already want. For example, if you’re trying to convince a developer to develop in a way that is minimally harmful to the environment, and you know the developer cares about money and not about the environment, you should show the developer how doing the environmentally friendly thing will make him more money. This might be because not doing the environmentally friendly thing will lead to expensive litigation down the road or because doing the environmentally friendly thing will win him support in the permitting process or for any number of other reasons. It is much less effective to try to show the developer that he should care about the environment.
This is true regardless of what you think about the developer’s valuing money over the environment and it is also true regardless of what you think about the arguments why doing the environmentally friendly thing will make the developer more money. What matters is not what you think of these arguments, but what the developer does. And this is true even if the developer knows that you don’t care about his making more money; the developer does care, and that is enough for him to assess your arguments on the merits and be persuaded by them if they are otherwise persuasive. If your goal is to convince the developer to do the environmentally friendly thing, then you need to link doing that thing to what the developer already cares about.
Another way of putting this is that it’s generally easier to convince people about means than it is about ends; it’s easier to convince them that they’ve misunderstood the best way to get what they want than to convince them to want something else entirely. It is not intuitive (at least it wasn’t for me before hitting the idea) that this is the way to go, especially when you yourself care deeply about the ends in question and think someone who doesn’t share those ends is deeply misguided or evil. But what you care about doesn’t matter; what they care about does.
I remember hitting this idea for the first time in some book in college; I don’t remember what book it was, but both the idea and the specific example are taken right from it. If I can teach you only one thing about persuasion — in front of juries, in sales, in recruiting, in finding witnesses, in fundraising, in any area where you want to convince someone to do something — this idea is it.