Everybody has plans until they get hit for the first time.
Commonly (and more satisfyingly) rendered as "Everybody has a plan until they get punched in the mouth."
Authentication Score 3
Citation
Tyson, Mike. "Tall Man Tyrell Biggs Thinks His Height will Add New Dimension to Oct. 16 Fight." Interviewed by Rick Warner. The Times and Democrat, 19 Aug. 1987.