on a 2 card board, I always calculate it in as a possibility. The thing is, the chances of them actually having it has never changed my decision.
now I know you said not a 3 card board, but even then, it is very rare that I would fold the boat when holding pocket pair or T+. Assuming the other cards on the board are lower then T. Granted I did do it once. It was because the player was very passive, and out of all the hands that I played with him. I bet him off the river about 80% of the time it got that far, and the other 20% he called. I had AA. and it was not a 3bet pot cause my raise was called preflop. He was in the blinds, and I was EP, and 99 came on the flop. Dry, unconnected board, he checked I bet, he called like always, J on the turn, that gave a straight and flush possibility, he bets the pot. Thinking he probably hit his J I call, or the smaller possibility he is holding a J9. For him to bet. He had to have J9, but I was willing to see it at showdown. I call hoping for a check, check river. 9 on the river. Instant shove....now I know that's a sign of weakness, but this guy never bet the river ever, even with straights on a possible flush board. And all the other times he instant bet he was holding a set on the flop. So in this situation I knew he had a 9. So I folded after tanking. Obviously since he was a terrible player and wanted everyone to see his quards, along with his "advanced" check call on the flop, he showed....
I turned to the guy to my left (who was very quite and hard to read) and said, "I folded AA."
His eyes lit up and he smiled and said, "wow I couldn't have done that! Nice job!"
Lets just say I not only took all the players chips that hit his quards, but I took the guy to the left of me too. Since he tried to bet me off every hand after that. Made a lot of money that night.