sins of omission

Sins of omission are wrongs committed by failing to act rather than by acting badly.

The concept comes from moral theology: you sin not only by doing harm but by neglecting to do good when you could have.

His sin of omission was staying silent when he should have spoken up.

The phrase extends beyond religious contexts to any culpable failure to act—the bystander who doesn't intervene, the official who doesn't report wrongdoing.

Contrasted with sins of commission, which are wrongs done through deliberate action.