Unless you have a flush/straight draw that you can place them on(that just hit), or the board is paired, then i'm going broke against a set with top two pair.

Always rember to look at what they would make that play with.

Against most players, because they will play so many hands like the nuts(overpair, TPTK, TPGK, bottom pair, flush/straight draw, etc) you cant fold top two pair.

I'll fold KK preflop 10 times before I will fold TPTK on a flop without a flush/straight draw out there. (and I'd still stay in against most players.)