The power of, "No."

It is one of the shortest words in the English language. Curiously it's the same word in several other languages. Two letters that when spoken with conviction convey volumes.
It's one of the first words that toddlers learn and then we forget what it means just a few short years later. Trials have been won and lost based on the intentions of the person who uttered the word. What did the person  mean when they said that word.
I had forgotten about its power too until recently. People would ask me to do things that I really didn't want to do and I would say, "Yes" when I should've said, "No." I should have been courteous. I could have said it respectfully, but the person was asking for something valuable: my time!