Why Do We Train

This has been a question asked time and again on Pat's blog among many others. Every time I came across one of these posts I would think to myself something along the lines of "to be better" or "because it's fun, duh" but lately I'm wondering if there's something more. I've wanted to learn martial arts (and Aikido specifically) from an early age. I wanted to learn so I could teach and spread Aikido to everyone I knew. Up until lately I've trained so I can be a better teacher, or at least so I thought. Last night while walking home from class I was thinking about it, and that's not why I train. Even when I don't have anyone to show anything to, I'm doing Tegatana or even Nijusan against an invisible Uke just to keep doing it. Playing the saxophone is fun to me, but I don't play anymore, so why Aikido? How come when I was on firewatch in bootcamp I'd shuffle step all the way up the deck, then all the way back? Why would I practice my collar chokes on my unsuspecting bunk mate, or take extra time to go to the gym to practice grappling? I don't plan on competing or looking for glory. Pat once talked about an exercise to get to the core of something where you keep questioning something over and over until you get to where you don't have an answer anymore. For instance, I want pizza, why? I want pizza because I'm hungry and I like pizza. Why do I like pizza specifically? I enjoy the bread, cheese and sauce due to taste, and because it's filling making me less hungry less often. Why pizza now and not a hamburger? I want a pizza just because I feel like pizza...that's all. If I apply the same thing to why I practice Aikido...I don't make it much farther than that. I could say it's for self defense, but that's not true. How often are people nowadays really in a situation they can not run or walk away from or avoid? I could say it's for exercise, but that's not true. I'm definitely out of shape :) I could say a lot of things, but I don't have an answer other than there are days when I'm excited going to class and days when I dread it. Either way, when I physically step onto the mat I cease being anxious, or sad, or anything. I just feel....like doing Aikido. I'm looking for an answer deeper than that, but I don't have one at the moment. What are some of the core reasons any of you train?