Time keeps on slipping, slipping, slipping, into the future. ('70s song ref. Bonus points if you can identify it. Extra points if you can do it without Google.)
Each year, I get a year older. By any reasonable estimate, I have already lived at least 2/3 of my life. When I thought about that, and how it would be to live my remaining years as my old self, I felt a wave of horror. That's when I knew I had to transition, I had to do it right away, and I had to make it happen as quickly as possible.
I remember that, when I was younger, the future seemed limitless. It no longer does. I am aware that there is a counter somewhere ticking down my days and years. When it reaches zero, it's game over. That's my motivator.
Transition is a joyful thing. Yeah, it's frustrating and painful, but the purpose is joy. See if you can find a bit of joy and hang onto it. Find something that makes you feel good, like maybe underdressing or dressing part-time in private. It can be a small thing, like getting your toenails done. Anything that makes you feel good. Then use that good feeling as your motivation to continue.