Year one of being a parent: I learned more about myself than in the previous decade.
Not all of it was flattering. Some of it I am actively still digesting. All of it was necessary.
A short list, in no particular order:
On sleep deprivation. I had thought I knew tired. I did not know tired. Tired is when your toddler — okay, infant — is screaming at 3:47 AM and you cannot remember which side you fed her on, or her name, or your own. The first time I forgot her name for half a second I was so ashamed I didn't tell my partner for a week.
On identity. For about four months I had no identity. I was a milk-producing, butt-wiping, song-humming organism. The reading-of-novels person I had been was on a long sabbatical. She came back. I'd been afraid she wouldn't.
On my partner. We learned that we are both, when sleep-deprived, sharper-edged people than we wanted to be. We also learned that we always come back to each other. That was good information.
On who you become. Slower. More patient about some things, less patient about others. Ruthless about your own time in a way that's surprisingly clarifying.
I would do it again. I would also tell my year-one self: it gets easier and you are doing better than you think.