Interesting idea from Eliezer Yudkowsky:

When someone asks you “Why are you doing X?”,

And you don’t remember an answer previously in mind,

Do not ask yourself “Why am I doing X?”….

Instead, try to blank your mind – maybe not a full-fledged crisis of faith, but at least try to prevent your mind from knowing the answer immediately – and ask yourself:

“Should I do X, or not?”