Somehow the sentence in the title sounds wrong: it seems to betray a lack of intellectual virtue—indeed, it suggests a vicious doxastic stubbornness. But surely there are cases where uttering the sentence is not a sign of vice. If the negation of the five minute hypothesis weren't true, I'd still believe it. I wonder if one thing that isn't going on here might not be this: counterfactuals of the form "q → I do A" are often elliptical for "(q & I know q) → I do A." And it would be stubborn to know that q isn't true and yet believe it (typically).