Here's one example from 1 Corinthians 9 where Paul expresses concern about maintaining self-control over his own body, recognizing that even though he is a preacher and an apostle, he could become a spiritual castaway if he neglects the Gospel and its teachings.
24 Know ye not that they which run in a race run all, but one receiveth the prize? So run, that ye may obtain.May we too seek to keep the lusts and desires of our bodies under control lest we fall into serious sin that pulls us away from Christ. It's a jungle out there and we need a little healthy paranoia about the dangers we face and healthy self-imposed restraints to keep us out of danger.
25 And every man that striveth for the mastery is temperate in all things. Now they do it to obtain a corruptible crown; but we an incorruptible.
26 I therefore so run, not as uncertainly; so fight I, not as one that beateth the air:
27 But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway.