when I first got my clipless pedals, I practiced with the bike in a stand...did not fall the first few times I went out on the bike...I was careful and uncliped well before any anticipated stop... I had done several rides before I fell the first time...came to a stop where the ground had a downward slop to the left...I had my right foot unclipped, while stopped I leaned left, started to fall and could not get my left foot out in time to prevent the fall... the left foot was unclipped before I hit the ground though...tuck and roll is important...
I was unhurt physically, but since there were lots of folks watching me fall, my pride was hurt a bit...
I have fallen a few times since and every damn time it was where people were watching...