"Be true to yourself" sounds like a license to set your own standards: whatever I choose is right for me. Charles Taylor argues, in "Inescapable Horizons," chapter IV of The Ethics of Authenticity [1], that the ideal itself rules that reading out.
His example: I may be the only person with exactly 3,732 hairs on my head, or exactly as tall as some tree on the Siberian plain. If I built my identity on that, you'd say: so what? Defining myself by playing the Hammerklavier sonata as no one else can registers at once, because music matters whether or not I pick it. A hair count doesn't, unless some story links it to something that does, like a society that holds the number sacred.
If choosing alone made something significant, every choice would weigh the same, which means none would weigh anything: choosing my path in life would count no more than choosing steak and fries over poutine for lunch. So the ideal of choosing yourself presupposes things that matter independently of the choice. Taylor calls this background a horizon of significance. His candidates for what must matter: history, nature, the needs of other people, citizenship, the call of God. The argument shows that some horizon is needed, not which one.
My first objection, which Harry Frankfurt defends [2], was that caring is what makes something important to you. The test between them: can your deepest caring be mistaken? If you can wholeheartedly care about something, later see it was shallow, and count that as learning rather than a change of taste, the caring was answering to a standard beyond itself.
My next worry was that a horizon lets the majority overrule the eccentric. It works the other way. The 1970s hobbyists building their own computers looked odd, and we now say they were right all along, not that opinion came round to them. That needs something they were right about, what computing could do, which was neither their choice nor the majority's view.
References
The Ethics of Authenticity [link]
Taylor, C., 1991. Harvard University Press.The importance of what we care about [link]
Frankfurt, H., 1982. Synthese, Vol 53(2), pp. 257–272. Springer Science and Business Media LLC. DOI: 10.1007/bf00484902