"In bad positions, the result of the best move is just as bad as the current position; moves that aren't the best move make things worse." (Ralph Betza, 1982). Feel free to quote me, but keep my name on it.
The practical application of this idea is that when you are in a bad position, as long as you can keep playing the best move things won't get any worse. If you make even the slightest mistake, you lose, but as long as you can keep finding the very best move every time, the game continues. If the other player makes a mistake before you do, perhaps you can draw or even win.
Many a time this idea has energized my play and allowed me to save hopeless games. "+-" is not "++", and "+-" is not fated to become "++": you can prevent the change by your own efforts.
Ah, but a larger advantage usually does translate into a larger winning percentage...