To cease to behave in a consistent and/or rational manner.
To lose sight of an important objective or principle; to act contrarily to one's own interests through concentrating on relatively unimportant matters.
Used other than figuratively or idiomatically: see lose, plot.
To make something ineffective, to invalidate.
To debase or morally corrupt.
To spoil, make faulty; to reduce the value, quality, or effectiveness of something.