You are literally living the law of sacrifice - especially in regards to giving up of yourself to become something that is more holy.

I could go into a lot of different reasons and details but at the end of the day serving a mission is a sacrifice no matter how you slice it.

I truly believe you gain so much more from a mission than you put into it. It's the greatest spiritual and life investment you can possibly make. But don't diminish the sacrifice aspect. It cheapens the effort and sacrifices that many make to take that opportunity to serve the Lord.