Middle pair example

[cmillard]

I was asked to give an example for the question about folding middle pair:
Say for instance I have J,9 in the BB with no raises. Flop comes K,J,5 rainbow. One person bets, the rest fold, I (normally call). If 4th and 5th street are checked, do I check? If there is a bet, do I automatically fold? Again, I realize it depends on the other player, I was just curious to see if there are any "general rules" to follow in this situation.
Thanks