When good security advice...isn't

Have you ever had one of those moments, while discussing security techniques with other clueful individuals, where one of you confesses to disagreeing with a common piece of advice? While it may be completely logical that you must account for context when giving appropriate advice, sometimes we may forget that we must also do this when we’re discussing security.

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Perhaps we should be asking ourselves more specific questions when we give others security decrees.

Is there any piece of common security advice that you find you disagree with?