What does it mean that the cue starts everything?

Without a reliable cue the rest of the habit loop never activates.

Example: A software engineer spends three weeks designing the perfect evening journaling routine — a leather-bound notebook, a specific pen, a sequence of reflection prompts — but never specifies when or where the routine should begin. She has no cue. Every night, the window for journaling passes while she scrolls her phone on the couch, and the beautiful notebook collects dust on the shelf. The routine is flawless in design. The cue is absent in practice. The habit never fires.

Try this: Select one habit you have been trying to build but have struggled to maintain. Write down the routine and the reward, then honestly assess the cue. Is there a specific, reliable, unavoidable trigger that initiates the behavior? If not, design one. Choose a cue that already occurs in your daily life with near-perfect consistency — finishing your morning coffee, sitting down at your desk, closing your laptop at the end of work — and write a precise implementation intention: "After I [existing cue], I will [target routine]." Test this cue for three days and note whether the habit fires more reliably than before.