Reversible Decision
also called Two-Way Door
A choice that can be undone cheaply, and which therefore deserves far less deliberation than an irreversible one.
Decisions divide roughly into two-way doors, which you can walk back through, and one-way doors, which you cannot. Choosing a logging library is a two-way door. Choosing your data partitioning key, your identity provider, or the boundary between two services is much closer to a one-way door.
The failure mode is spending equal time on both. The discipline is to move fast on the reversible ones — the cost of being wrong is one refactor — and to slow down, prototype, and write an ADR for the irreversible ones.
Reversibility is itself a design variable. An abstraction layer, a feature flag or a strangler facade can convert a one-way door into a two-way one, and that conversion is often worth paying for.