Before you waste it on anger, resentment, spite or envy, think of how precious and irreplaceable your time is. Positivity always pays off.
Your feelings are a gift. Sometimes you just need to patiently unwrap them so you can find the important message inside. When you feel it, you heal it.
Never underestimate the pain of a person, because in all honesty, everyone hurts. Some people just hide it better than others.