The inversion, in one sentence

Here is the whole of the next lesson compressed into a line, and it is worth reading twice.

You are waiting to feel like doing something before you do it. In depression the feeling arrives after the action, not before it.

That is not a motivational slogan. It is a description of the order things happen in when reward has been stripped out. Waiting for motivation in a depressive episode is waiting for a bus on a road the buses no longer run down.