Everybody Has It
Whether you're a mongoose avoiding a snake, or a dude sitting on the crapper, any time your neurological system has too much input, it freaks out.
This is the essence of the startle response.
The idea is, if there's way too much for me to handle that probably means it's dangerous, and my body freaks out to get as much distance between me and whatever is happening.
Physiology to the Rescue
Any effective self defense system has to address this detail. You can't keep it from happening, so you have to incorporate, adapt, and learn how to nudge your startle response in the right direction.
But, all the training in the world isn't going to keep you from dropping your phone in the toilet. #BrowseResponsibly