Perhaps? Can you think of a counter-example, where seeing an event happen once is more attention-getting and memorable than seeing the event happen twice in a row in quick succession?

Imagine you see a herd of deer trotting along, and one goes down. A hole, or ditch, or maybe a predator? Now imagine two deer go down at nearly the same time. Different implications, or at least different probabilities to the possible implications.

I'll stand by my over-generalization for now, but I'm open to counter-examples.