I hear what you are saying and where you are coming from. I took offense with those kinds of off-handed sayings for a long time too. Then I had this thought to see them as affirmations and encouragements.

I interpret "Be Yourself" as saying..... be true to yourself; be your authentic self; be-lieve in yourself;

As for 'Fake it until you make it'. It can be motivational for me. If I determine to act in the way that expresses my true, authentic and affirming 'self' it will cut into the voices that tell me otherwise.

I feel like a do a lot of performing (faking it). I find it very difficult to 'be myself' even with the positive messaging. I hear the messages but still find myself in the trap of being someone else I think will be more welcomed than my true, authentic self might be.

I think.... now that I ramble about it..... I think it is complicated. lol

I also think it is great to ask the question. It prompts further examination. At least it did for me. Thanks