I hate throwing away "won games." It's worse than getting completely slaughtered -- and is much more psychologically devastating.
Here's a good example.
I am playing black and the winning move (against a much higher ranked opponent) is right in front of me.
1. . . Re2+ is decisive. Black's key worry (indeed, only worry) in the f6 pawn.
1. . . Re2+ nips it in the butt. The white king cannot retreat to the d-file (shaded area).
2. Kd7 (for example) is met with 2 . . . Rf2!. And white's last pawn is gone. (White cannot play 3. Rxf2 because of 3 . . . h1 = Q.)
But Black can't retreat to the f-file either.
If so, white's king is trapped there and black has free reign to advance his queen-side pawns to promotion. (ex. 2. Kf7 is met with 2. . . c4).
How is the white king "stuck" on the f-file?
If White moves to the g-file (ex. 3. Kg6 it is met with 3 . . . Kg2+!).