Situations where you prepare diligently but still fail because a core assumption is wrong or you didn’t appropriately weight a truly dominant factor. Especially likely to occur in cases where it’s more comfortable to focus on the familiar instead of looking to unearth the unfamiliar, uncomfortable point that could invalidate all your diligent preparation. (This is most cases.)

Examples:

• “Fighting the last war”, e.g. French perfected static defences in Maginot Line, but Germans developed blitzkreig tactics to bypass them.
• Focus on technical merits of a project over non-technical aspects like distribution, politics that may be more likely to truly determine commercial success.
• Childcare research - evaluating lots of factors like physical environment, food, curriculum etc but dominant factor is whether child will get along with the educators. Alternate formulation, maybe difference between centres is relatively trivial and the same major challenge of settling will occur in any centre.
• Somewhat related to the idea of the straight-A student who diligently studies for tests, but isn’t equipped for ‘real world’.