I had one game in which I made a move to start an attack. I was so confident the ensuing complexity is better for me. My confidence must have been shown in my action. My opponent looked at me and thought for about 15 minutes. Both of us were class A players. He could not believe that I made a simple blunder. He'd rather believe that I had some plan hatched out, so he chose a simplified response. Instead of up by a whole piece with no compensation for me, he just gave up a key pawn for my piece. This in fact led to a more active position for me and I won the game in the end.
When a stronger player is losing, sometimes s/he tries to swindle the weaker opponent. S/he will make moves so forcefully and quickly as if s/he is already winning. The opponent may be so intimidated that s/he began to make weaker moves and the game might be reversed, especially when time is short for both sides.