By St. Gregory of Sinai
Those who seek humility should bear in mind the three following things:
1. That they are the worst of sinners,
2. That they are the most despicable of all creatures since their state is an unnatural one,
3. That they are even more pitiable than the demons, since they are slaves to the demons.
You will also profit if you say this to yourself:
"How do I know what or how many other people’s sins are, or whether they are greater than or equal to my own? In our ignorance you and I, my soul, are worse than all men, we are dust and ashes under their feet."
From The Philokalia, Vol. 4.