What if there is doubt about the boundary between a mistake and unacceptable behavior?

Do not treat doubt as evidence against the person concerned. Gather additional facts, have someone with expert knowledge look at the real options for action and test whether others could have made a similar choice under the same circumstances. Distinguish between what is visible afterwards and what the person could reasonably have known at the time.

Record the trade-off and remaining uncertainty. A drastic personnel measure requires a more rigorous and independent process, with a hearing and an opportunity for reconsideration. In addition, resolve system weaknesses immediately; disagreement about individual accountability is no reason for a demonstrable safety problem to exist.