A domino can knock over another domino about 1.5x larger than itself. A chain of dominos of increasing size makes a kind of mechanical chain reaction that starts with a tiny push and knocks down an impressively large domino.
Original idea by Lorne Whitehead, American Journal of Physics, Vol. 51, page 182 (1983).
for sophisticated discussions of the physics.
As seen on QI in the “kinetic” episode. I was contacted by those Elves.