if one knows what’s good for one
if (one) knows what's good for (one)
If one wants to avoid trouble (one will do or avoid a certain thing). Oh, you'll be on time for the meeting, if you know what's good for you. If he knows what's good for him, he'll stop calling me that.
if one knows what’s good for one
phr. one had better do what is expected of one. You’d better be on time if you know what’s good for you.