Definition
This idiom is used to advise someone to have fun and enjoy themselves but also to be cautious and avoid taking unnecessary risks.
Kids, go have fun, but remember, be good, and if you can't be good, be careful.
I know you're looking forward to the party, have a good time, but remember, be good, and if you can't be good, be careful.
College life is an amazing experience, enjoy it, but remember, be good, and if you can't be good, be careful.