What does it mean that the routine is the behavior itself?

The routine should be clearly defined so there is no ambiguity about what to do.

Example: Marcus decided to build a morning writing habit. His cue was specific — after pouring his first cup of coffee — but his routine was "write more." Some mornings he opened a journal. Other mornings he stared at a blank document. Occasionally he edited old drafts and counted that. The habit never solidified because "write more" is not a routine — it is an aspiration wearing a routine's clothing. When he redefined the routine as "open Day One, set a timer for ten minutes, and write without stopping until it rings," the ambiguity vanished and his streak began.

Try this: Choose one habit you are currently trying to build. Write down the routine as you currently conceive of it. Now apply the script test: could a stranger read your description and execute the behavior with zero interpretation? If not, rewrite the routine until every physical action is specified — what you open, where you sit, how long you do it, and what signals completion. Read the rewritten version aloud. If it sounds like stage directions, you have it right.