Our mouth can be two things: a Band-aid or a Hammer.
When a friend is sad or hurt, if you say good things ("it'll pass," "you're great," "I'll help you"), your mouth is a Band-aid. It helps heal the boo-boo in their heart. That's being a "Tree of Life." But if you say mean things ("you're annoying," "nobody likes you"), your mouth turns into a Hammer. It hits your friend's heart and "breaks" their joy (crushes their spirit). Nobody likes being near someone with a hammer mouth.