There is usually at least a tiny grain of truth hidden somewhere behind even the most absurd belief. For example, if you lend a book to someone, you might as well kiss it good-bye. You won’t get it back without asking for it back, and maybe not even then. If you’re a library, you’ll probably get it back; but for anyone else, lending books is about the same as giving them away.
What is the belief? People don’t return borrowed books when they borrow them from other people.
There is a grain of truth here. Some people aren’t good about returning borrowed books and perhaps that’s most people, depending on who you lend your books to.
Is this true on average? I don’t know and doubt that you know either. Even so, I believe it. How about you? Do people return books other people lend to them?
Now suppose that I ask you to lend me a book. If you think people don’t return borrowed books, you might give the book to me, not expecting it to be returned. However, if you think people are good and usually return borrowed books, you still may not lend it to me, depending on the value of the book to you. But why?
When we make choices involving other people, we are always playing the odds, using our own idiosyncratic computational system. We attach odds to their doing or not doing something, the likelihood of their behaving one way or another, the probability of their reacting as we expect or surprising us instead. Our action, behavior or involvement with them then depends on those calculations. First comes the calculation and then we act, based on our nearly instantaneous decision process.