// week 02 · day 10 · fri

Build the Investment Argument.

$/business-case · ~25 min
// 01 · what it does

The argument and its stress test.

business-case builds the argument for or against an initiative: problem-first framing, quantified opportunity, impact sizing with explicit assumptions, a cost model (engineering, opportunity, infrastructure, and ongoing costs), a risk assessment, alternatives considered including Do Nothing, and a recommendation with stated confidence. Then it stress-tests the entire argument with a premortem, a blindspot check, and a conviction assessment.

The stress test is what separates business-case from a pitch. A premortem asks: "It's 6 months from now and this initiative failed — what happened?" A blindspot check asks: "What am I assuming that I haven't examined?" A conviction assessment asks: "On a scale of 1–10, how confident are you — and what would change that score?" These three questions force intellectual honesty before the argument goes to leadership. You'll get a stronger business case by surviving the stress test than by avoiding it.

Day 10 is the Week 2 capstone because it pulls together everything built this week. The discovery plan mapped the problem, the feedback synthesis provided user signal, the data analysis provided quantitative grounding, and the competitive work provided market context. The business case is what happens when all of that becomes an investment argument.

// 02 · sample prompts

Two ways in.

prompt.basic.txt 
/business-case

Build a business case for adding a wishlist feature to our app. Users frequently ask for it in reviews. It would let them save listings they're interested in and come back to them later. We're a small team — 4 engineers — and this would take about 3 weeks to build.
prompt.advanced.txt 
/business-case

Build the case for investing in the adventurer repeat engagement loop at Terrain.

Problem: once an adventurer completes their first booking, Terrain has no structured re-engagement mechanism. No post-experience push notifications, no personalized suggestions based on past activity, no mechanism to share a completed trip. The 38% adventurer repeat rate (adventurers who complete 2+ bookings in a 12-month window) is entirely organic — adventurers who come back do so because they remember Terrain, not because Terrain brought them back.

Evidence:
- Day 7 feedback synthesis: "I forget to come back unless I'm planning a vacation" was a distinct recurring theme across NPS verbatims and adventurer interviews. Source distribution: adventurer NPS (3 instances), interview notes (2 instances), post-booking survey (1 instance).
- Day 8 data analysis: adventurer repeat rate signal — 38% current (target 45%). No current cohort analysis on time-to-second-booking, but the data analysis flagged this as a data gap worth closing.
- CAC is approximately $38 per adventurer at current scale. A 7-point improvement in repeat rate (38% → 45%) would add approximately $609k GMV annually at current MAU without incremental acquisition spend (calculation: 47,000 MAU × 7% more repeating × $185 average booking value).

Alternatives to consider: Do Nothing (organic repeat remains at 38%); purely promotional re-engagement (email/push campaigns with no product changes — low build cost, likely low lift); full social layer (trip sharing, friend graph, wishlists — high build cost, long timeline, not committed to).

Ask: build the case and run the full stress test. I need to be able to defend this recommendation to Dana Park (VP Product) next quarter.
// 03 · reflection

Three questions.

  1. 01What did the premortem surface as a failure mode you hadn't considered — and how would you mitigate it?
  2. 02Where did the skill's conviction rating land — and do you agree? What would move it up or down by 2 points?
  3. 03What does the Do Nothing alternative tell you that the build case doesn't — and is it actually a viable option?
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