The following game against a mid-1500 rated opponent shows what I was talking about in the post on Dan Heisman.
To begin with he played a gambit I’m not very familiar with so I ended up playing into a position where Fritz and Houdini engines said my position was inferior by 2-3 P’s. In a couple of cases I disagree with their evaluation, but obviously I’m not good enough to prove it. In any case, what interesting is the position after I played 20…g5. White grabbed the P and attacked my R on d8 without hesitation then after 21…Rg8 realized I was threatening mate and his B was pinned. As the engines pointed out, he should have played 22.h4; that would have lost a B for a P but at least he had some dim hopes.
But wait! There’s more. After 24.Re6 my Q doesn’t have any escape squares and I have to return the piece to save it and we end up with an equal position! Even if White failed to notice that point he would have been able to play on and make me work for the win. Instead he made a couple meaningless threats (22.d5 and 23.Rab1) and repeatedly refused to play the obvious defensive move. I’m guessing that the mate threat and loss of a piece instilled him with panic and he was no longer thinking clearly.
I see this time and again even in my own play against stronger opponents. Stay calm and focused! You can’t afford to relax for even one move, especially if you have an inferior position. Easier said than done though.