Duolingo entered high-stakes English testing, then math, music and chess — from a language app. Each entry reused something and rebuilt something, and the interesting part is which was which. This skill packages that judgement into patterns you can run against your own next bet.
Structured as a graph: scan the descriptions, follow only the [[wikilinks]] you need. Don't read all ten up front.
Choosing what to enter
- [[references/intensity-of-demand-beats-market-size]] — rank candidates by evidence of self-organization, not by addressable population.
- [[references/repeated-inbound-requests-are-the-spec]] — demand from your own users removes the reach risk and the trust risk at once.
- [[references/demand-hides-in-your-own-data-and-your-users-misunderstandings]] — stated interest at scale, informally-served categories, and recurring misconceptions as roadmap signals.
Where to attack an incumbent
- [[references/attack-the-axes-the-incumbent-cannot-move]] — move price, duration, place and format together; size by who is priced out.
- [[references/optimize-for-the-side-nobody-has-served]] — in a two-sided market, the side that endures the category is unclaimed value.
- [[references/port-the-incumbents-goal-not-their-safeguards]] — their controls compensate for constraints your medium doesn't have.
What transfers and what breaks
- [[references/port-the-method-and-the-format-vary-the-subject]] — method and artifact shape are portable assets; vocabulary comes from the destination.
- [[references/check-whether-your-core-abstraction-survives]] — the unnamed invariant your pipeline rests on, and where fan-out justifies depth.
- [[references/wire-the-second-line-into-the-existing-habit-currency]] — one daily slot, one counter; a second currency builds a rival, not an extension.
How to commit
- [[references/validate-in-the-cheapest-shape-first]] — fake the connected parts, prove it on one surface, reuse existing material for reps.
Not in scope
Pricing and packaging the new line once you've decided to build it — free tier, paywall placement, plan design — belongs to the monetization skill, not here. Whether the shipped version clears your quality bar is [[../duo-product/SKILL]]. Motion, tokens and component craft route to the external design-engineering skill.
Sibling skills
- [[../duo-product/SKILL]] — taking the long view, shipping, and raising the bar on what you just entered.
- [[../duo-growth/SKILL]] — turning a new line into acquisition once it exists.
- [[../duo-experimentation/SKILL]] — the testing discipline behind "validate in the cheapest shape".
- [[../duo-retention/SKILL]] — the habit machinery a second line either feeds or fragments.
Sources
Distilled from 22 posts on blog.duolingo.com (2020-06-11 through 2026-07-14), all cited inline with dates in the nodes above; accessed 2026-09-22.