Have you ever been in "a mood"? More specifically, a bad mood. Someone asks, "what is wrong" and you say, "Nothing specific, I am just in a mood.". Let's take that logic and flip it. If you can simply "be in a mood", then why can't that mood be "a good" mood. That is what "Joy" is. It is an attitude that we choose to have, despite our circumstances. That is why God encourages us to have the "attitude of Christ".
Lord, help me to be an encourager to others but also to myself so that I can be in a position to be an encourager to others.