The phrase, "be yourself," is a double bind. It's a command to be spontaneous; when, spontaneity has to be a choice made of one's own accord; if even that. It's something you just do. Society is riddled with such situations; which, is probably why people are constantly tense, frustrated, and have a general feeling of dis-ease. It's been this way probably since the beginning of there for a way to be; and it will probably continue on as long as there is a way to be.
There is no way NOT to be yourself; you are already doing it. Even if you are being a complete, utter, fake, phoney; you, are being yourself, and probably doing what the majority of people are doing. The people who are really playing at, 'being themselves,' couldn't tell you how to do it, any more than some one could explain to you in a few words how to play Bethoven's Piano Concerto No. 5. Worse than that, at least there are probably instructions to eventually learn how to play the Piano Concerto No. 5. You won't find a book or tutorial in the world that covers how YOU, specifically you, can and should go about being yourself.
Accordingly, my words will fail just as well. I don't know how to, 'be myself'. I care what others think when I shouldn't and probably don't care what others think when I should. I put others before myself, often at my own expense. I self deprecate constantly. I feel all sorts of guilts and shames for things, I really perhaps shouldn't give a honeysuckle about, if not, to a certain modest degree, celebrate. The list goes on. Yet, those are the things my, 'self', is doing, so how is that not being me? It's still me playing at not being the real me.
However, that's no excuse to sit it out instead of dance. It's no excuse not to ask a pretty girl out, even if I fear making a fool of myself and getting rejected. It's no excuse not to take leaps of faith for my life in the direction I'd like to take it; paths I choose not to go down for fear of whatever failure or calamity might ensue if things don't go right, etc.. etc.. Just because you are being yourself when you are not being yourself doesn't mean you get a free pass at not being yourself. You know what's inside of you, and, THAT, is what tears you up inside. It's what eats away at, probably, ALL of us, in one form or another, even though the forms of others may be hidden from us or indistinguishable at different moments.
Perhaps even those who give such advice and seem to be able to do the, 'dance', themselves, must have their own problems. What's the use of knowing how to dance the Tango if you've no partner to dance with? To me, I guess, sometimes the sun shines, and other times, the clouds block out the heavens; but, where I live, it's nice to get rain. Other places, it rains more than not, and it's nice to get clear skies..
It's just one of those things. No one can tell you how to do it, and there is no way to figure out how to do it; and yet, it must be done. Right?