... is not 2 years, contrary to the old joke!
A crossdresser is a man who likes to pretend he's a woman sometimes. A transsexual, is a woman who's been forced all her life to pretend that she is a man.
It is a subtle, but profound difference. It's subtle enough that often it is hard to tell one from the other, especially in a society that can't acknowledge that there can sometimes, rarely, be a mismatch between the gender of your mind and the sex of your body. From most cisgender people's perspectives, only the first statement is possible.
I've talked to some CDs who seem to view me as a supercharged version of themselves, someone who puts on an act that lasts forever - where I make permanent changes to my body to enhance the part I'm playing.
In fact, it is quite the opposite. I'm myself now for the first time in my life - my life as a man was a total lie. The changes to my body are to correct horrible disfigurements caused by a life lived with the wrong hormones going through my body. My life now is the most real thing I've ever experienced. My life before transition feels more like a dream, and not a pleasant one.
One of the things I'll say about transition is that if your goal is to physically change to better play a part, you are almost certainly transitioning for the wrong reason. On the other hand, if you find yourself choking on saying the phrase "I'm a man who likes to pretend he's a woman sometimes," then perhaps that is not, in fact who you are.
