I constantly questioned "Am I really sure I know what I'm doing?" really often earlier in transition. I only seriously considered stopping once, though... Right before I finally got my first post-transition job.
A week before my first job finally came through, after having been fired from two jobs due to dysphoria (one because I made an inexcusable mistake while experiencing high amounts of dysphoria-related emotional distress, one because of outright discrimination,) I hit rock bottom. I applied for a job back with the same company that I'd originally been with, I had the chance to get back everything that I'd lost, the same pay, the same benefits, a full-time schedule, same city, same friends who I missed so much. And I got an interview. All I had to do was make it through that panel interview. I failed. I wasn't "upbeat and positive" enough, because I basically froze during the panel interviews due to being so terrified of how other people were judging me.
That was the only time that I seriously considered stopping. Because at that point I had now been unemployed for 5 months straight, I'd been rejected from 5 straight jobs, and what felt like my one chance to get back what I'd lost was gone for good. I seriously considered stopping. Because I thought that I'd destroyed my employability, that I'd never get another decent-paying job again, that my entire education and entire livelihood was going to waste, and I had the worst emotional breakdown I've ever had, because the thought of giving up was too painful, but so was the feeling of failure and rejection.
Fortunately, a week later, I got my current job, I've been there for almost 2 years now, and now there's no way in hell I'd ever go back. After a few months of working there, I started getting into that state of mind where my current self is me, I can't even remember being male anymore, to even think of not being this self is unthinkable. That comes once you settle in.