First-Principles Reasoning
Reducing a problem to the physical, mathematical or economic facts it rests on, then reasoning up, rather than reasoning from analogy or convention.
Analogy says "companies like ours use Kafka". First principles asks what the actual requirement is — durable ordered delivery of X events per second with Y retention and Z consumers — and then asks what satisfies it, which is sometimes Kafka and sometimes a database table.
Where it earns its keep in architecture is the latency and capacity questions, because they bottom out in physics and arithmetic that nobody can argue with. Light travels about 200 km per millisecond in fibre, so a Mumbai–Virginia round trip cannot go below roughly 60 ms; a disk seek costs what it costs; a single connection can carry so many requests. Those facts settle debates that opinions cannot.
The discipline is knowing when to stop. Re-deriving everything from scratch is slow and arrogant. Use it when the conventional answer is expensive, when the situation genuinely differs from the one the convention came from, or when the numbers do not add up.