Comparisons
Pairs engineers genuinely confuse — goal and implementation, MVP and bad prototype, prototype and spike, reversible and irreversible. Neither column wins; what decides is the problem. Each record leads with the confusion, because the confusion is what it costs.
Build vs buy
The decision is made on licence cost against engineering hours, which are the two least important numbers. Buying carries an integration cost, an operating cost, an outage plan and a dependency on someone else's roadmap; building carries the maintenance forever and the regulatory burden nobody counted. The store that spends three weeks on its own payment processing has bought nothing and built the wrong thing. The strongest form of build is that a provider's abstraction never quite fits and the seams become the product's bugs; the strongest form of buy is that operating infrastructure is a full-time job the team does not have. The questions that decide it are the same either way: is this core, can a provider solve it, what does integrating cost, what does operating it cost, what happens when the provider fails.
When the capability is your differentiation, when no provider fits a hard constraint (data residency, latency, cost at your volume), or when the small version is genuinely small.
When the capability is a solved problem someone else operates well — payments, email delivery, object storage — and the integration and operating costs are honestly counted.
| Aspect | Build — write and operate it yourselves | Buy — integrate a provider or a product and operate the integration |
|---|---|---|
| Right when | It is your differentiation, or no provider fits the constraint | It is a solved problem with an operator |
| Hidden cost | Maintenance forever; compliance | Integration, operating, the outage plan |
| Failure you own | All of it | The integration and the fallback |
| Example | Your ranking, your pricing rules | Payments, email, object storage |
| Question that decides | "Is this why customers chose us?" | "What happens the day the provider is down?" |
| Sign of the mistake | Three weeks on payment processing | A provider chosen on licence price alone |