Comment by zentiggr

Take an example with only two fireflies. Their clocks won't be at the same point at first, of course.

So one lights up... and the instinct is for the other firefly to try and light up at the same time. How?

Since it was going to light up later than the first fly, it shortens its cycle a little bit and lights up a little sooner.

Repeat that cycle a few times and soon enough, the second fly has 'caught up' and is flashing when the first one does.

Add more fireflies, and its just more of the same. When a nearby firefly lights up, the ones close by speed up a little. Eventually, they all converge on the 'fastest' time.