h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I read a wonderful analogy once for how solitons work.

Imagine a group of people of various levels of fitness running along a long mattress. Each runner produces a small dent in the surface where they are currently running.

The fastest runners are at the front of the group, and the slowest at the back. However, because the mattress bends, the group as a whole creates a dip in the mattress.

So the fastest runners at the front are always running 'uphill' (and hence slowed down a little), and the slowest runners at the back are always running 'downhill' (and hence sped up a little).

So the group tends to stay together!