“So just do it” is a glaring one for me.
Simply because it is disregarding someone else’s thought processes and how their mind works. Where simply ‘just do it’ is not as easily and readily accomplished. This kind of advice is always uttered when one person is going on about how they’re tired of something and want to do something else. So this gets mentioned.
It could be a lot of reasons as to why, even if it is down to the obvious reasons. My valid reason a lot of the time is that I just don’t have the energy or will to just magically get myself to do something.
What “Be yourself” means is: “Don’t pretend to be someone else because you think that will make you more appealing. It will likely show through that you’re not that other person and your attempts at deception will drive away the people you want to attract. Further, if you find that being your authentic self is something you are ashamed or embarrassed being, perform some introspection on what those things are about yourself you don’t like and take action to change on things you can. Examine rationally whether the thing you think is shameful is something you even have control over. For example, are you ashamed because you’re not tall? You have no control over that one. That is nothing to be ashamed of. Are you ashamed because you don’t have good hygiene? That one you DO have control over. If you don’t know how to correct that, ask for help and get to the place where you won’t be ashamed of your hygiene. You will ‘be yourself’ that is not as tall as you like, but with good hygiene.”
That’s a lot to say so it gets boiled down to “Be yourself”.