[Here is] advice from Rabbi Simcha Bunam, a Hasidic rabbi who lived in the late eighteenth and early nineteenth century. He told his students that they should keep a note in the right pocket that said for my sake was the world created and in the left pocket a note saying I am but dust and ashes. When feeling down, take out the note from the right pocket. When feeling full of oneself, take out the note from the left.

Greg Marcus in The Spiritual Practice of Good Actions