I think that you need more information in order to correctly choose whether to lay down your hand. Here are two scenarios:

1) There was no raise preflop. You get top two pair and you are playing from late position. An average player who is slightly loose with average aggression bets from the big blind. Reraise and be willing to go all-in. Since there was no initial raise preflop and this player is playing from the big blind and raising instead of check-raising he probably has two smaller pairs (pretend in this case that its a KQ5 flop and you have KQ.

2) You are in late position. There is only one limper in early position. You raise with AT and try to steal or isolate the tight passive in early position. It doesn't work and you get the small blind and the early caller. The flop comes with AT3 with two diamonds. Both of the players check to you. You bet out pot size or so. One player from the sb folds. The other player is in early position and now reraises you 3x your bet. This player is very tight and passive. He would only call a bet from early position with a pocket pair. He has a set of 3s or Ts and has you beat. Lay the hand down. Of course he could also have AK but he probably would have reraised.

Alias you need to keep track of hands like this and post the exact hand history so that we can analyze it and give you a better answer. There are many variations that each have a different correct choice based on the exact situation.