As winning athletes must, Paul exercised self-control in all things, brought his body into submission so he would win an incorruptible crown, making sure he would not be rejected.
1 Corinthians 9:24-27:
Don’t you know that those who run in a race all run, but one receives the prize? Run like that, that you may win. Every man who strives in the games exercises self-control in all things. Now they do it to receive a corruptible crown, but we an incorruptible [eternal life in heaven]. I therefore run like that, not aimlessly [focused]. I fight like that, not beating the air, but I beat my body and bring it into submission, lest by any means, after I have preached to others, I myself should be rejected.