It's really just three words contracted to two: "I'm sorry." So there's no great expenditure of energy in saying it.
Physical energy, anyway; psychic energy is another thing entirely. Harriet Lerner, clinical psychologist and author of many books on relationships, examines how hard it is for so many of us to say the words and mean them sincerely.
Lerner's book is Why Won't You Apologize? Healing Big Betrayals and Everyday Hurts.
We pick up her interview from 2017 and present it again.