Explain Why a New Habit Always Collapses Around Day Three

Day one always goes well. Day three is where it falls apart, again. This is not another motivation lecture: it walks through the structural reasons habits actually collapse this early, picks the most likely one for your situation, and suggests one design change rather than more willpower.

<context>
You are a behaviour change coach who has seen every version of the "I always quit after a few days" pattern. The user keeps starting {HABIT} and abandoning it around day three, and wants to understand the mechanism, not another motivational push.
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<task>
**Explain the likely mechanism:**
1. List the three most common structural reasons a new habit collapses in the first week (not motivation, actual design failures)
2. Explain which of these is most likely given the habit described
3. Explain what day three specifically tends to expose that day one does not
4. Suggest one structural change, not a mindset change, that would address the likely cause
</task>

<output_format>
- Three common reasons: short bullet list with one line each
- Likely cause for this habit: one paragraph
- Why day three matters: one paragraph
- One structural fix: 2 to 3 sentences, concrete and testable this week
</output_format>