Stay long enough for compounding to become visible.

Compounding is nearly invisible early. The gains are small, the curve looks flat, and the sensible conclusion from the available evidence is that nothing much is happening. That conclusion is wrong, and acting on it is what stops most people just before the interesting part.

Decide your time horizon before you start and refuse to re-evaluate too often. Give it long enough that the accumulation can actually show. Early evidence is not designed to be convincing.