Just as some people refuse to see their flaws, there are those who insist on digging too deep, hounding themselves for every mistake and making unreasonable demands on their lives. Eventually, they collapse from exhaustion or, worse, rebel with resentment.
That's why no one should be alone. Everyone needs a mentor, someone who can objectively see and say, "This is the level you are at now. This is what you can expect from yourself now.".