Cobbler, stick to your trade.

proverb Do what you are familiar with, experienced in, or skilled at; don't attempt, interfere with, or give advice about something you are unfamiliar with. After his failed attempts at writing books and hosting a television show, many think the aging DJ should retire or return to radio. Cobbler, stick to your trade. Look, I know you are trying to help, but you don't actually know the first thing about computers. Cobbler, stick to your trade. College today is wildly different than it was 15, 20 years ago, so I tell parents of college-age students all the time, "Cobbler, stick to your trade."