Do your best in all things even the ones you don't want to do
The only way to grow intellectually is to challenge yourself and work on your weaknesses, avoiding every situation but the ones you're best at will lead you down a narrow and unsatisfying path where you might not ever realize some of the best things about yourself.
"Don't be good at the things you don't want to do."
If I don't want to do something, I'm very likely not going to do it.
do your best
I do my best to be the best at everything I do