You hear people say it all the time.
I've heard myself think it, except I don't actually hear myself think anything. Wait, if I don't hear what's going on in my head, do I "feel" it going on in my head? Umm...I guess I've sensed that particular pattern of neurons firing inside my cranial cavity.
The idea is kind of like that Aristotelian idea of the ideal form of things. (or is it Platoisticish? Dang, intro to philosophy fades away from the mind like shadows on a cave wall, amirite? Wait, yeah it was Plato, because "Platonic Idealism" is a thing. Yeah.) Here's how I think some folks think about it, and how I thought about it for many years:
And don't try to suggest my Self might be screwed up, because it's perfect. I can't even talk that way to myself.
Of course, being "authentic" doesn't work out so well, partially because it causes undue stressful chronic overthink, causing me to ask myself all sorts of unanswerable questions:
On top of that, obeying the "authentic me" basically means doing what I want, when I want to, all the time
So, you're authentic self doesn't have to agree with me, but my authentic self believes that "being true to yourself" doesn't actually mean anything.
So, I don't try to be "authentic" I just try to be consistent.
Oh, wait - that doesn't mean anything either, because stubborn consistency can be a huuuuge problem.
I guess probably the best goal is this: I'll try to not consistently be a sucky person.