It depends. If your going against someone that's really making you think, and you blunder or have a mouse slip, there is little chance of winning. That's especially true with a mouse slip. But it mostly boils down to the position, regardless of how the blunder was made. The lower the rating of the players, the more likely the opponent will blunder later in the game, if the game lasts long enough, and at least even up the game again.
It depends on the position, if you are attacking and have possibilities of checkmate or compensation of your loss then you should keep playing. otherwise it would be a waste of time.. analyze your situation, dont be hopeless, try to to see if there is a 4-5move variation to compensate it. btw compensation may be material or positional advantage..