Here it is an explanation of the catch-22 taken from the wikipedia:
"In non-psychological circumstances, the phrase "catch-22" (based on the book of that title) has come into popular use to describe a less formal style of double bind, a cyclical conundrum, or "no-win situation". A Catch-22 situation, like a double bind, is also inherently self-defeating: the very act of trying to solve it prevents it from happening.
A double bind occurs when the following hold true (this is a less formal description, the technical description is given in source references). Because of the nature of his/her situation:
The person must (or cannot) do X.
The person must (or cannot) do Y, which conflicts with X.
Any commentary on the absurdity or untenability of the situation is strictly forbidden.
Thus the essence of a double-bind is two conflicting demands, neither of which can be ignored, which leave the victim torn both ways in such a way that whichever demand they try to meet, the other demand cannot be met. "I must do it but I can't do it" is a typical description of the double-bind experience. It demands that they solve what is (to them) an unsolvable unavoidable problem."
So what do you have to do is to find something related to a "must but I can't", "no-win" situation. That's the catch.