My story is similar to a couple others posted here, but I'll tell it anyway. I managed to fall off three times in the span of about an hour.
When I first started riding with my sister-in-law, she made me ride bareback so I could develop good balance. I went to get on the horse in his pen, climbed up the fence rails to get on, and just as my weight shifted away from the fence, he stepped sideways, and I landed in the manure between him and the fence. Ha ha ha, horsie, hilarious. So I climbed back up the fence, got ready to get on again, and anticipating the same move, I leapt for it. Well this time, he didn't step sideways, of course. If anything, he may have slightly shifted toward the fence.
So I sailed over the other side, onto the ground again. Third fall was trotting in the arena, made a sharper turn than I was ready for, and I went off the side. Fun times!