[inigyou]

But what if it becomes relevant?

An uncertain reward is a strong motivator in psychology. You give a rat a lever that drops a food pellet, he'll push it when he's hungry. You give a rat a lever that drops a food pellet 5% of the time, he'll keep pulling it, build up a little stockpile and then gorge himself.

You give a rat a lever that does nothing and drop pellets at random times, he'll practically pull it until his arms fall off.