[Doctor_Fegg]

And the upshot of (iii) is that you have to start swinging that bell _before_ the preceding bell has sounded.

This is called "ropesight" and is the hardest thing to grasp about bellringing. Essentially you need to watch, out of the corner of your eye, every other ringer in the chamber: typically six bells in a village parish church, eight in many town churches, 12 or even more in a cathedral. When you've identified which ones should be sounding before you in the sequence, you need to make sure your bell is swinging a fraction of a second after theirs. To do this you need to watch their movements, listen to the pace of the bells, and have full control of the speed you're swinging the bell.

For an experienced ringer it's second nature. But it's the hardest thing for a beginner to learn.