Haven't read this book, but I was born female, and I still don't know what makes a man. I generally just go with "I'm a man because I say I am and look the part and it says M on my license." But people can disagree.
I've transitioned now and am stealth in real life, which means nobody knows my past because I hide it. I don't really have any problems now unless I'm interacting with people who know about my past, usually from my past (people aren't always accepting).
But back before I transitioned, I had a lot of problems. For starters, I was just in pure denial until about age 20. I joined the military and there had about the same amount, but different types, of problems. I had a group of really good friends while in who knew my predicament, and there were definitely many times I sat down crying because I'd never have a penis, and without a penis, I wasn't a man. Even if I got the surgery and everything. And one of my buddies would sit down next to me and say, "CurrentID, you're more of a man than I am," and he'd listen reasons why (related to military stuff). That guy helped me not kill myself too many times. It wasn't all good stories though and too many stresses piled up and tl;dr suicidal actions got me out of the military in 2012.
Anyway, I've been on testosterone since 2012 and had top surgery in 2013. I'm 27 now. Almost all my stresses were gone as soon as I separated from people who didn't see/treat me as a dude. I had more problems than just the gender thing, but my therapist just recently cleared me for once a month meetings! Before I was doing once a week for 6 months, then once every 2 weeks since.
In the beginning, I overcompensated and tried to be the manliest man possible because everyone has a different definition of what it means to be a man, if you don't hit all the marks, people will still say "You're a girl" and that doesn't hurt when you know you're a man, but when there is still an inkling of a doubt, it messes up your entire self-identity.
Nowadays I am just myself and not projecting an image of what people think might qualify as a man. To me, I am seen as male and I'm legally male. Anyone who doesn't agree can get the fuck out of out my life. We're all the better for it.