Good suggestions!

(1) When you suspect that the sunk cost fallacy is in play. Even if you understand the implications of the bias, it’s really difficult to objectively evaluate a situation once you’d paid heavily toward a particular outcome.

(2) When you’re uncomfortable with thinking about ways your situation/project/idea might fail. This is similar to your #2, but it takes the onus off yourself. Sometimes your own weaknesses have little or nothing to do with the flaws of a plan, but that doesn’t mean it makes sense in the long run.