From Longman Dictionary of Contemporary Englishknow your limitsknow your limitsinformalKNOW somebody to know what you are good at doing and what you are not good atI know my limits. I’m not an administrator. →limit
Examples from the Corpus
know your limits• The Profitboss does so much and no more, knowing his limits.• These lunchtimedrinkersknow their limits, or at least most of them do.• I know my limits, and I'm not a great runner.• Ford says she may be good at her job, but she knows her limits.