'Be yourself' is advice given by those who don't really have anything useful to say to you.

'Be yourself' is a lazy fallback expression people can say to sound supportive and wise, when they either don’t really give a shit, or have no experience or useful advice to give about the subject matter. Stop asking these people for advice, and start finding people that can and want to help you become excellent - not just to be mediocre.

The best is the enemy of the good.