TechniqueDecision principleProductFounders and companiesDecision-making
Ask about what people already did, never about what they would do
Rob Fitzpatrick · The Mom Test
The idea
The rule Fitzpatrick's book is named for is that your mother will tell you your idea is good, and so will everyone else if you ask them whether it is. Questions about the future produce flattery; questions about the past produce facts. Ask what someone did last time they faced the problem, what it cost, what they tried, and who they paid. The answers tell you whether the problem is real and worth money, without anyone having to be rude. The Library calls it the most portable idea in the technology collection, and it travels well beyond product work into diligence of any kind.
Evidence about demand comes from what people have already done and paid for, not from what they say they would do.
When it works
Customer discovery, commercial due diligence, and any interview that asks how you would validate a product idea.
When it may fail
Past behaviour cannot show demand for something genuinely new, which is where the technique is weakest. For those cases the evidence is a commitment, time or money, rather than an answer.
How to use it
Rewrite every would-you question as a did-you question before a customer call. Would you pay for this becomes what did you pay for last time, and how did that go.
Where it came from
Book The Mom Test · Rob Fitzpatrick
What the source says. A short, practical book on customer conversations that do not produce flattering nonsense, whose named rule is the most portable idea in the collection.
Connected ideas
Says something similar
A board that accepts a narrative has stopped doing diligenceA compelling story is a claim to test, and the test for a technology is watching it work.
Says something similar
Shipping is an output. Nobody is paying for outputsMeasure what changed for the customer, not what was shipped; a team given an outcome behaves differently from one given a list.
Concepts
Put it to work on L3VLUP
More like this
- TechniqueProductVideo located
A metrics question is a structured hunt: north star, guardrails, then the segment
Clarify the metric, protect the guardrails, then decompose the drop by segment until it is isolated; show the process, not a guess.
From Google Product Manager Metrics Interview: A Worked Mock · Aakash Gupta
- FrameworkLeadershipLetter
Day 2 begins when a company manages to proxies and treats decisions as one-way doors
Check whether the metric is still the goal or has become the goal, and reserve the heavy process for decisions that cannot be undone.
From Amazon's 2016 letter to shareholders (Day 1) · Jeff Bezos
- FrameworkInvestingFilm
A cheap measurable signal beats an expensive intuitive one at scale
The market misprices what is hard to measure, so a consistent cheap signal can beat an expensive expert.
From Moneyball · 2011
- Decision principleDecision-makingBook
A good decision and a good outcome are separate things
Judge a decision by what was knowable when it was made, and keep the outcome in a separate column.
From Thinking in Bets · Annie Duke