Standing on a narrow ledge, afraid of falling, you might feel a strong urge to jump. Why?

It actually makes a lot of sense, from a survival point of view.

Consider - you are standing on a ledge. You tell your brain that you don't want to jump. Your brain immediately responds with a plan for how to jump off the ledge. Possibly several plans (you can jump by bending your legs and suddenly straightening them; you can jump by leaning forward and shifting your centre of gravity over the hole; you can jump by stepping on a roller-skate and falling down).

When your brain gives you several ways to fall off the ledge, you then know of several things to avoid - you need to move carefully, lean away from the hole if possible, and avoid stepping on things that will move. If your brain gave no importance to those plans, then you would be more likely to fall into the hole by sheer negligence; not looking where you put your feet, for example. (How often do you watch where you put your feet when it's not important?)

Admittedly, actually following the urge would be suicidal; but merely having the urge may well improve your chances of safely leaving the ledge.