To question reality during the dream, you have to have more interest in questioning reality than in what is happening during the dream. So being interested in questioning reality during the day is a good start no matter what conclusion you come to.

When you do a reality check during a dream and it fails, as long as you have enough attention to notice the reality check failed, enough memory to remember that a failed reality check means you're dreaming, and enough expectation for a failed reality check to mean you're dreaming (to trust the conclusion you come to), the reality check will work.