Sticky ideas have to carry their own credentials. We need ways to help people test our ideas for themselves —a “try before you buy” philosophy for the world of ideas. When we’re trying to build a case for something, most of us instinctively grasp for hard numbers.

Compact ideas help people learn and remember a core message. But they may be even more important when it comes time to help people act properly, particularly in an environment where they have to make lots of choices.

We’ve seen that compact ideas are stickier, but that compact ideas alone aren’t valuable—only ideas with profound compactness are valuable. So, to make a profound idea compact you’ve got to pack a lot of meaning into a little bit of messaging. And how do you do that? You use flags. You tap the existing memory terrain of your audience. You use what’s already there.

If we’re trying to persuade a skeptical audience to believe a new message, the reality is that we’re fighting an uphill battle against a lifetime of personal learning and social relationships. It would seem that there’s nothing much we can do to affect what people believe. But if we’re skeptical about our ability to affect belief, we merely have to look at naturally sticky ideas, because some of them persuade us to believe some pretty incredible things.

The lesson for the rest of us is that if we want to make people care, we’ve got to tap into the things they care about. When everybody taps into the same thing, an arms race emerges. To avoid it, we’ve either got to shift onto new turf, as Thompson did, or find associations that are distinctive for our ideas.