This is timely and beneficial. Most of the posts I see on HN about job changes focus on the external conditions of a job that cause misery. However, as you've pointed out, these situations also have a positive side—they offer opportunities to develop inner virtues: truth, endurance, persistence, and others.
Had you posted this just two months ago (and had I managed to take it to heart), I might have saved myself from disappointment and regret. I quit my job after going through a six-month stretch of burnout. I thought I had nothing left to give, and that staying would do more harm than good—for both myself and my team. When you've been in that kind of negative mental state for an extended period, your decision-making skills become compromised. I began to believe my negative thoughts and feelings, and I couldn’t see a way past them. When I left, I used words different from "leaving to do what I love," but the sentiment was similar.
I'm now considering asking for my job back, though I’m unsure whether it will succeed. I was told I left on good terms, but I wonder if that was simply a reflection of good business etiquette from my boss and coworkers. I’m afraid I may have shown myself to be unreliable, despite a solid four-year track record of consistent performance. I also don’t know if I’ve learned enough to keep myself from relapsing.
Another thing often left out of these kinds of posts: what supporting factors help a person persevere? Friends, family, hobbies, religion—pursuits they can turn to for some respite? One of the thought patterns that contributed to my burnout was dwelling on the amount of competition and dishonesty in the world, when perhaps I should have made more room for gratitude.