A failure mode is a specific way a plan can break: a wrong assumption, a missing number, a dependency on something untrue, or a step that does not survive contact with an opponent.
The term comes from engineering, where analyzing failure modes means enumerating every way a component can fail and how badly it hurts. A plan has failure modes too — they are just written in prose instead of tolerances.
Naming a failure mode is more useful than a vague worry because it is specific and actionable: it points at the exact assumption to fix, not a general unease.
Every BadMars finding is a failure mode, anchored to a verbatim quote from your plan and ranked by severity and probability. They are drawn from a coded taxonomy of the failure modes that recur across real plans, so the report reads like an engineer's failure analysis, not an opinion.