For this, we have a sort of cascade effect to thank; the more stuff left tumbling around up there, the higher the chances of a collision.

Don't we see this cascade effect rather a lot in sport: an initial success inspiring others to reach for the same?

The above can cause a cascade effect when multiple trains become stopped at the end of each block.

Note that disconnection can, unfortunately, have a cascade effect, leading to overcurrent in other circuits that then also must therefore disconnect automatically.

Other investors begin to participate, leading to a cascade effect.