For me, it was mainly a lack of sleep, and doing something I do every day without turning my brain back on. No real difficulty, just not paying attention to what I was doing... being careless. Kinda like if you walk enough, eventually you'll stub your toe on something... not that walking is difficult... like mentioned above, there are those that have fallen, haven't fallen but will, have fallen and will fall again. I can track stand for a handful of seconds, but when you're caught off gaurd, it's difficult to regain balance! Or it is for me at least.