“Be yourself; everyone else is already taken.”

This was written by Oscar Wilde

Now what does it mean?

Meaning

Be yourself. Simple

All that you'll get from trying to be someone you're not or even trying to be someone else entirely is only going to give you tiredness, exhaustion, and a lack of purpose.

Be yourself. I don't care if you like yourself or not just knowing that you are being yourself or at least trying makes you more unique and interesting as a person already so why change and risk losing that?