How can one falling domino start a row?

Tick, tick, tick! A tiny push at one end of a domino row can make the far end fall. Yet the first domino never travels to the end. Each piece stays near its own place while the falling travels along the row.

A standing domino needs a nudge to tip. As its top moves over, gravity pulls it down. If the next piece is close enough, the falling domino touches it and gives it a nudge too. That piece tips into its neighbor. One small meeting leads to the next.

A wide gap changes the story. A domino falls flat before it can reach the next one. The pieces beyond the gap keep standing. They are ready to fall, but the nudge never arrives.

The first push is not doing all the work. Someone lifted every domino when setting up the row. Each raised piece has stored energy that can be released as it falls. To send the falling along the row again, all those pieces must be stood up again.