I had read this quotation many years back and have recalled it many times in life. Today again I read it and find it so true.
"Don't flatter yourself that friendship authorizes you to say disagreeable things to your intimates. The nearer you come into relation with a person, the more necessary do tact and courtesy become."
The Autocrat of the Breakfast-Table,
1858US author & physician (1809 - 1894)