I just thought of a real one. My granddaddy used to tell me, don't put anything on paper that you don't want everyone to read. I really took that one to heart. I can't even keep a journal.
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"If you have men who will exclude any of God’s creatures from the shelter of compassion and pity, you will have men who will deal likewise with their fellow men." — St. Francis of Assisi, 1181-1226