They believe in their own self-interests, in an overly optimistic faith in their own abilities and judgments, and that they're smarter than the average bear, as Yogi would say.
For example, virtually everyone who dabbles in the stock market knows that asset price bubbles exist even if they are constantly denied by paid shill bankers, economists, and the media, but that they have no real choice but to play along by a psychology of materialism, and that they will be smart enough to get out near the top.
Its a journey, not a comfortable sofa. Your ticket doesn't say where you're going, and the crowds around you are not your friends. Make something up, make a life out of it. Lots of people want somebody else to make it less scary and control everything. Just ignore them there isn't enough time to waste on that.
Do what you can, cross your fingers, and then take your dirt nap like we all must do. We'll just see.