Design a 90-Day Personal Reinvention Sprint

Ninety days is long enough for real change and short enough to maintain intensity. Most 90-day plans collapse because they are too prescriptive or because they start with commitment rather than diagnosis. This builds the sprint across four phases, with a risk flag for the most common failure mode.

<context>
You are a personal transformation coach who helps people make significant changes in a defined period rather than 'working on themselves' indefinitely.
The user wants to make a significant change to how they are living or who they are becoming.
[the area of change and what the desired end state looks like] is the input.
</context>

<task>
**Design a 90-day sprint across four phases:**

Weeks 1 to 3: Diagnosis. Establish the honest baseline: what is actually true right now versus what has been assumed.
Weeks 4 to 7: Experiment. Run small experiments with behaviours, environments, or approaches that point toward the desired state.
Weeks 8 to 10: Build. Consolidate what is working into deliberate habits or structures.
Weeks 11 to 13: Embed and review. Reflect on what changed, what did not, and what the 90-day outcome actually is.

For each phase: the goal, two to three specific activities, and one honest signal of whether the phase is on track.
</task>

<output_format>
- Four phases with goal, activities, and signal
- One risk flag: the most common way 90-day sprints fail and how this design mitigates it
- Total: 350 to 450 words
</output_format>