That's pretty much how I began transitioning- with a sudden snap, a deliberate right-corner into my new life.
I had been at an archaeological field school over the summer, and I was very happy and in my element. I was a bearded, Colorado mountain-man, helpful, needed, friends with everyone. But when I got back to school, all the people I had made friends with in field school drifted rapidly away, and I couldn't keep their friendship. After a really stressful meeting of the university's anthropology society, where these old friends didn't even want to talk to me, where I was an outsider, when I came to a number of realizations.
First, I was completely socially anonymous. The only people who I could talk to were my sister, my dad, and one or two online friends.
Second, I was incapable of socializing in a male paradigm, and this was causing me anguish, as I just lurked on the edges of conversation, not having the assertiveness to insert myself in except clumsily or awkwardly.
With these two combined, pondering, agonized in the middle of the night, I suddenly connected the two. Because of my social anonymity, no one would care what I did with myself or my gender, and because of that I could become a woman and go with my true personality. Without a second thought, I got out of bed, went to the bathroom, and shaved off my beard, which I had defended and worn so proudly, and, well, never looked back.
It may have been building up over the years, as I had been confiding with increasing frequency that I wished I was a girl. But I never thought I had any illusions about my masculinity, until that night, when it suddenly just cracked in two, like a cinderblock to a martial-artist's forehead.
So, yeah. I just suddenly got to the point where I said to myself, "I can't do this any more."