Roll back. Two four letter words.
When I first learned to drive, some of my time was spent driving using a manual transmission car, and other times using an automatic transmission. The biggest difference between the two wasn't learning to shift or not - it was a difference, but not a huge one. The biggest difference was how to handle stopping on a hill. Or more specifically, starting again when you were stopped on a hill.
For most stops with an automatic transmission car, there was no real problem. The car didn't roll backwards as long as you were in drive - and you stayed in drive as long as you were... well... driving.
But on even a slight hill in a manual you had to play a quick game with your feet, engaging the clutch with your left foot so it was at just the right point to hold you in equilibrium, taking your foot off the brake because you needed to apply it to the gas pedal and then slowly nudging the entire vehicle so it would move forward. Do this wrong... and you'd find yourself rolling backwards down the hill - usually towards the car behind you that had started advancing already. But do this right... or at least mostly right... and you would defy gravity and move forward.