People.

"You see, the truth about people isn't very hard to understand. The ones who stay, stay because they want to. Because they feel the need to. Because they care and don't want to see you alone. They'll always be there for you and you never have to ask them why. While the ones who leave, leave because they must. Because they received what they wanted from you. Because they no longer see the need in having you around. And almost always, do they leave unexpectedly. It's sad but you see, the truth about people is simple. You should always grow with the ones who stay and learn from the ones who leave... and let your heart and time decide which of the two is worth remembering."