I was gong to make simplicity a category of its own because it does not completely fit under solitude but since I did not have enough content I will leave it here for now.
Simplicity has to do with living a simple life - or living without all the extras.
It could also be classified as self-denial, abstinence, or just doing without. The goal of it is to set our focus on God instead of being caught up in materialism. I would tend to disagree with the extreme asceticism of some monks who would whip their bodies, starve themselves for long periods of time, expose themselves to extreme cold and other such extreme practices. Like always, I prefer to balance one discipline with another. Celebration is the discipline of enjoying all that God has given us.