Just like cycling, really. I remember having a three speed Sturmey Archer bike & it was a simple job to stop & pedal half a turn back and click it from third to first. When I got a bit more serious & a racing jobbie with lots of those derailleur thingies, it was a practiced art.
But when you mastered it, you could keep the leg cadence at a pace & swap the cogs to suit the load.
Some people seem to have issues with the concept though..
