Smell the tactics coming in :)
Amit mentioned in a comment elsewhere that we don't know when there's tactics in the position on the board.
That is indeed an important difference between solving tactic puzzles and looking at a position at the chessboard during a game, where there might or might not be tactics possible.
However, I am convinced that most chess players can develop a sense to feel when there might be tactics in a chess position during a game.
Let's a have a look at it with a puzzle from a game I've just played, black to move and win :