Iron has the most stable nuclei because of... chemistry reasons... so it was thought most radioactive decay chains would effectively end there. This is also neat on an astrophysics level because iron is the last element created by first generation stars, so you'd get this grand entropic cycle that ends with a universe made of black holes, neutron stars, iron, and loose hydrogen atoms, more or less. In theory but not practice, probably.

For all human practical purposes decay chains end in lead though. The time scale in the meme is the difference between "effectively stable" lead and "as stable as possible" iron.

Tl;Dr everything below iron will get fused into at least iron by stars. Everything above will decay into iron.