Everybody has a plan until they get punched in the face!

That great American pugilist Mike Tyson was once asked about whether it worried him that his opponent was training hard and seemed to have developed a fight plan against him. Tyson respond with something to the effect of "Everybody has a plan until they get punched in the face".

So true. Once you get knocked back on your heals, everything changes, with your plans often getting scrapped in the process.