I was always confused because I sort of assumed guys would think the same way I do despite all the evidence to the contrary.  I think when I accepted I was trans it was like a big light bulb lighting up in my head saying ooooh that's why they don't behave the way I do.
With that said though I think I understand men even less now though then I did before.

I think I actually understand guys slightly more now, but I'm not that far into transition.  Before accepting that I was trans, I just always subconsciously assumed men felt like me and were just lying about it.  Kinda funny that I was that dense and never figured it out, really.