Structured brainstorming, and ranking the ideas
Lenses that make your ideas complete, and a simple way to choose between them.
Key takeaways
- A strong brainstorm is a short, organized list: first pick two or three buckets that cover the space, then fill each with ideas, then say which idea you would test first.
- Common mistakes: Listing ideas in random order.
- The buckets make the list complete and easy to follow. Then fill them with ideas.
Key idea
A strong brainstorm is a short, organized list: first pick two or three buckets that cover the space, then fill each with ideas, then say which idea you would test first.
| Lens | The buckets | Good for |
|---|---|---|
| Internal and external | Things the company controls; things in the market, competitors, or rules | Why something happened |
| Short and long term | Quick actions (weeks); structural changes (months or years) | What the client could do |
| Stakeholders | Customers, employees, suppliers, partners, regulators, competitors | Reactions, risks, and public-sector cases |
| Value chain | Buy, make, move, sell, serve | Where a cost or problem sits |
| Revenue and cost | Ways to earn more; ways to spend less | Profit improvement ideas |
So-what
Choose one lens, say it out loud, then fill it. The lens shows the interviewer that your list is complete.
- Fewer visitors
- Internal (the museum)
- Price rose
- Same exhibitions for years
- Shorter opening hours
- External (the market)
- Fewer tourists in the city
- New competing attraction
- Building works near the entrance
Internal and external as the first split, then a few ideas in each.
Ranking ideas by impact and feasibility
| Easy to do | Hard to do | |
|---|---|---|
| High impact | Do first (quick wins: fast, cheap, clearly useful) | Plan carefully (big bets: large gains that need time and money) |
| Low impact | Do if cheap | Drop |
So-what
End every brainstorm by naming the one or two ideas in the top-left box.
Worked case
A Singapore bank wants more young customers to use its credit card
The prompt
What could the bank do to get more customers aged 20 to 30 to use its credit card?
The structure
- More card use by young customers
- Get the card to more young people (acquisition)
- Make holders use it more often (usage)
- Keep them from switching to rivals (retention)
Working it through
1. Acquisition ideas
Instant approval in the app; partnerships with universities and first employers; a welcome bonus in SGD for the first three payments.
2. Usage ideas
Rewards on the things young people buy often (food delivery, ride-hailing, streaming); easy split-bill features; making the card the default in mobile wallets.
3. Retention ideas
No annual fee for the first years; spending insights in the app; fast customer service in chat.
4. Rank them
Rewards on food delivery and ride-hailing are high impact and easy (partners exist). Instant in-app approval is high impact but harder (credit checks and systems). No annual fee is easy but lower impact alone.
The recommendation
Start with rewards on everyday spending and default placement in mobile wallets: quick to launch and aimed at how young customers pay. Plan instant in-app approval as the bigger project.
Listing ideas in random order. Giving ten ideas with no ranking. Spending three minutes on one bucket and none on the others. Offering ideas that do not fit this business (a luxury brand launching discount coupons).
A gym chain in Mexico City is losing members. Using a lens of your choice, give two buckets and two ideas in each, then say which idea you would test first.
What is the first step in a structured brainstorm?
An idea is high impact and easy to do. What should you do with it?
Which lens fits best for "Why are our costs rising at a factory?"
Sources for this lesson (1)
- Recognized public explanations of case-interview concepts and frameworks
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