Drive or Addiction?

As I was out running the trails this morning I couldn't help but ask myself...what is it that makes a human want more? Is it drive or addiction, a little of both or something completely different. When is that we can say ok I am satisfied now and if we do say that is that settling? I thought about all aspects of this.....I don't believe a alcohol or person who continues to use drugs continually wants more because of drive so that has to be an addiction. Just one more drink or one more pill. I have always struggled with my weight and lost 85 pounds in 2004. For the most part I kept it off. I look at times when I say ok...10 more pounds. Throughout the years of keeping this weight off I at times will gain 10-20 of it back....it seems like once I have gotten to a certain weight I almost settle Like I have reached a goal and now I don't need to try anymore....at this point it starts to creep back on until I will tell myself enough is enough. I will give myself all the excuses in the world as to why I put the weight back on to justify it and it works and it sounds like very reasonable reasons to anyone that listens. At the end of July I said enough was enough and now have taken off about 31 pounds so I am currently at the lowest weight I have ever been....but I want more. I tell myself I want more because I am training for this ultra and I already have a ton of disadvantages due to knee and foot issues so I have convinced myself that the less I weigh the easier it is going to be on my joints....and this is true. I am far from being too skinny so there is nothing to worry about there! I do ask myself if I am wanting more out of fear? Out of fear for settling and accepting where I am and then using that again as a reason to not maintain. I think the word maintain and settle are so similar and I don't ever want to be known as someone who settles.
I then start to look at the wanting more aspect of endurance sports. I have done 3 Ironman Triathlons, several marathons, over 20 half Ironmans but I still want more and have always told myself I want more. Is it about testing the limits of our body, our mind? I do know that I am always needing and wanting to be training for that next goal and after reaching that goal I immediately start to ask myself what is next? I do not feel at all like I have something to prove to anyone because there really isn't anyone to prove anything to. It's almost like I just need to see if I can do it. Personality wise I have always been an insecure person...I wonder if that has anything to do with "proving" to myself what I am capable of doing?
TO BE CONTINUED AT SOME POINT