For Pascal the first rule of human thought or behavior is that we are not what we were meant to be. God did not create us to live lives shrouded by doubt, but sin has distorted even the faculties that give us knowledge. That means that understanding who I am according to the Christian story means understanding that I am, fundamentally, fallible. I know that my desires can distort the way I see the world. I know that my reason can become prideful and dogmatic, and lead me into error. So for Pascal, and here he echoes Augustine, doubting myself is sometimes just good common sense. It’s thinking rightly about my own limitations in light of the distorting effects of sin.