What is prospective memory failure?

Example: You decide to do a breathing exercise every time you sit down at your desk after lunch. Three weeks in, you realize you have not done it once — not because you rejected the habit, but because you never noticed the cue. Sitting down had become so automatic that it produced zero attentional signal. You place a bright orange card on your keyboard before you leave for lunch. Now you cannot sit down without physically moving the card — and the trigger fires every time.

This concept is part of Trigger Design in the How to Think curriculum.