I think this question will really vary depending on you're asking, because people's motivations and life goals are all different even if the process is superficially the same.
I don't consider myself transgender. It's too broad of a term which encompasses lots of definitions, and makes it a bit blurry for me. For me the phenomenon is very specific and the term I would use is transsexual, because it describes my experience accurately. For various reasons which may be attributed to various dimensions, including, but not limited to: social, cultural, biological, etc, I leaned towards the feminine in almost everything, which made living as boy impossible without causing everyone a lot of confusion, perplexity from those around me. I also suffered from body dysphoria. I transitioned because I realized, over time, that given the cards I had been dealt with and body dysphoria I felt over the things that made me (yuck!!!) biologically male, I knew I would live much better as a girl, and later, woman.
Additionally, the fact that not all male secondary sex characteristics developed me for me (such as a low voice, beard, broad shoulders, muscles, etc) due to reasons I never cared to further investigate, that made it even harder for me to fit in the world and know where I belong to. But made it extremely easy for me to make the leap and live as a woman. It was extremely easy to integrate in groups as girl. Suddenly, everything was so smooth. I started voluteering in a orphanage, when I was 18. I showed up (was still not out to everyone), had been on HRT for two months and the first time I entered the orphanage, a girl was walking out of the truck, she worked there, and I asked her if I was at the right place and she referred to me as a girl, and I froze. Will always remember this moment. I wasn't wearing makeup, had short curly hair still and didn't even wear a bra, was with a sweatshirt. But she didn't even hesitate. I then presented myself to everyone as a girl and on that day I was sure I could live as a girl all the time. Before HRT, I already confused people.
What made it harder for me to transition was my parents, who insisited on not accepting and not coming around. They finally did and paid for my SRS on September 2017. I am forever thankful that they did accept. I think having a family who accepts and supports rather than tolerates or hates who you are makes a big difference on how well adjusted you become, after transition. Being passable can obviously be very important. I just wanted to go on with my life and now I rarely think of it.
Transsexual for me is only a medical term. I live as a woman and, therefore, being a woman is a part of my identity just like having dark hair or green eyes is. I don't think of it any other way. Transition is temporary, that's why it's called transition. For me, social transition was over when everyone in my circles either accepted me as girl or only knew me as such (and therefore it became impratical to tell). It's not a term I like to flaunt, and that is my right. Just like someone who has had some kind of cancer (excuse me the analogy) does not have to hold as a badge if they don't want to (but they certainly can if that's their wish). Medical transition was over when all my secondary and primary characteristics aligned with female.
Overall, I couldn't be happier with how my transition went, even if I had a very rough start because of lack of support which made everything 10 times harder, but I wouldn't have lived many adventures, if it had been another way, so there's a good side to everything.
sorry for the wall of text, TDLR: transsexual describes the medical experience better, so I opt for that term but do not use on a daily life basis, so much written to have it sumed up like that lol