The prayer of Examen isn't a new concept to me, but it's one I have practiced only rarely. I avoid looking within. The maxim "know thyself" kind of terrifies me, honestly. I'd rather not plumb the depths of my sinful self.
But this prayer isn't really about introspection or navel-gazing. It is about looking back over the day (or week, etc.) and first, searching for how God was present to us throughout the day and how we responded. Secondly, it is about inviting God to go with us into a review of our day and to show us the places where we fell short and sinned. Only by revealing those dark places can we find healing and growth into Christlikeness.
I appreciate Foster's way of handling this topic. He isn't shying away from the difficulty of it. The revealing of sin is painful. But he spends a good bit of ink revealing the grace of it. The grace is in self-knowledge. He explains that we can only offer to God our true selves - not what we'd like to be, or what we seem on the surface to be, but our true, actual selves. That includes our brokenness, our weakness, our tendencies toward sin.