I imagine this is where the phrase "one bad apple ruins the whole batch" but it sounds like in practice, a good apple can also help get the whole batch ready, a

I imagine this is where the phrase "one bad apple ruins the whole batch" but it sounds like in practice, a good apple can also help get the whole batch ready, all the while getting old and tired. Not sure if there is any wisdom in that but it feels like it could have some. Something about teaching and getting old doing so?