don't rest on your oars

Don't relax or become idle after achieving a goal. I know you're happy to have won the election, but don't just rest on your oars. You need to start planning your first act as class president now. I know your first novel was a smash success, but if you just rest on your oars, you're going to fade into obscurity. I know your company has been extremely popular for the past decade, but don't rest on your oars, or you'll be surpassed by smaller companies doing more interesting and innovative stuff.