There's a lot of stress and strife in this world. The people you surround yourself with intentionally, that you care about and share things with, shouldn't be part of that stress.
—Erin Nicholas in She's the One
People come into your life for different reasons. Some are forever, but those are rare. Most people are seasonal—they're with you for a reason and when that reason is fulfilled, they move on.
Erin Nicholas has the following books quoted on Quodid: