Once, again.

One workout doesn't change anything. It might make you feel better (or worse). But by itself, it has no significant impact on the body.

A hundred workouts do.

The catch is that you can't reach a hundred without the one. Starting (or restarting) - getting the first version done - is the hard part. The second version becomes easier once we ship the first.

Habits are formed by doing things once, and then again, and again.