Interesting question! I'm probably 50/50.
- attempting a skid at high speed as a kid, and ignorantly using the front brake! (too much brakes)
- hitting an invisible log in thick grass at high speed (no brakes)
- hitting an invisible curb at medium speed (no brakes)
- hitting a car at high speed (not enough brakes)

and probably a few instances of coming down stairs, or over tree roots or something and locking up the wheel at slow speed. I wouldn't expect ABS to kick in there though - in some of those situations it might actually be better to just lock it, like if there is some incredibly dangerous obstacle up ahead, like a cliff.

Steve