Is 'be yourself' really such great advice?

what if you think that the person should, in fact, change something about themselves…this is if they’re asking you about what they should do in a relationship or a friendship…I don’t believe in the whole ‘oh we’re just human, people make mistakes’ reason for all things…I do think people should identify flaws within themselves or understand their flaws when made aware of them and they should strive to be better people…so much stagnation is caused by people thinking that others should just ‘accept’ them and while acceptance is necessary in that no one should be discriminated against based on things like race or sexuality but people should be ‘bothered’ if others think they’re mean or cheap or stupid…