Clinamen. The Latin name Lucretius gave to the unpredictable swerve of atoms which occurs at no fixed place or time. Atoms move straight down through the void by their own weight, deflect a bit in space at a quite uncertain time and in uncertain places, just enough so you could say that their motion has changed. But if they didn't swerve, they would just fall, like rain and there would be no collision. And nature would not have produced anything.
Lucretius would have this indeterminacy as providing the "free will which living things throughout the world have".
Sometimes, as we fall through life, we collide with a person who alters our motion. The collision may be only brief as you move together for a moment, sharing space and time and food and wine and ideas and hopes.
But better to have swerved and collided than to have never swerved at all.