This is the thing about thoughts. You can't control them, even when your whole being rests upon them. Modesty flies out of the cage as soon as you think about doing something nice for the people you love. In order to realize that your worries aren't even the tiniest fraction of their sorrow, your mind needs to learn that they have suffered more. In a way, you seek joy in their sorrow. Tittle tattle, life works that way.
A pure mind is a myth because every saint sins.