It's when the sun shines through them that you notice how much your windows need to be cleaned. Nevertheless, it's best to wait for a cloudy day to clean them, because the direct sunlight will dry up and clump whatever cleaning agent you use, and you will find yourselves in a frustrating battle with smudges and streaks.
In the same way, it's when we most feel the presence of God in prayer that our sins and state of distraction comes most sharply into focus. But this isn't the moment to dwell on or work through such troubles. We should just enjoy and appreciate God shining upon us, however imperfectly we receive Him, and not give in to the temptation to turn back on ourselves. There will be plenty of dimmer moments to work out our plans for ascesis and the means to increase our recollection.