From Feynman's Six easy pieces:
Then a molecule leaves it is due to an accidental, extra accumulation of a little bit more than ordinary energy, which it needs if it is to break away from the attractions of its neighbors. Therefore, since those that leave have more energy than the average, the ones that are left have less average motion than they had before. So the liquid gradually cools if it evaporates
Why do the molecules which are left have less motion? I can't understand why. Is it because there are fewer molecules for them to jiggle against and get more speed? Could someone please explain? Thank you in advance.