So, when you think about asking someone out, their worthiness is a random variable to you. You have some idea of their quality, but you aren't sure of it because you don't know them yet. (that's your prior belief).
But, let's say you ask them out...assuming that high quality people (at least some the highest quality) turn you down, that implies that anyone who accepts a date with you, your idea of their quality immediatly decreases (your posterior). i.e., anyone who accepts a date from you is pretty much automatically not as good as you thought they were before you asked them out.
It's so true. It's thinking, "Well, if they'd go out with ME, that means they are not as good as me" -- because people always want to aim higher. Therefore, anyone who resorts to dating you is not good enough for you, even if you've previously placed them at a high quality when perhaps they would not date you.
It also explains the so-called "thrill of the chase" -- if someone agrees to date you/kiss you/whatever, you no longer want to be with them, because obviously you can do better.