I've never really questioned why I exercise and limit my dietary intake. I feel better from doing it. I'm healthier and happier with myself. But I really don't sacrifice all that much in my lifestyle. I drink regularly, but just not to excess (I can't remember the last time I got drunk or was hungover). I eat what I want to and my diet is fairly loose, but I've never been what you would call a big eater.
I've always had good eating habits (I was raised that way). Condition-wise I'm really not in the same league with many T-Nation posters. I don't want to get big. I do have fitness goals, and ultimately I plan on being about 190-200lbs with a low body fat percentage (around about 10%), but this is a goal I'm pursuing at a very leisurely pace.
So far I've managed to put on ~5lbs of LBM per year over the last 3 years. This is a pace I'm happy with and given that rate of progress I should be about where I'd like to be in about 2 or 3 more years. If I tightened up my diet and put more dedication in at the gym I could meet and exceed my goal in a shorter period of time, but I'm happy with my current plan and progress for a couple of reasons:
1) I like to eat (easy diet), relax (enjoy a drink when I feel like it), and otherwise enjoy life. This limits my progress somewhat, but I continue to make progress that I'm happy with and I don't feel like I'm sacrificing the good things in life.
b) At my age (40) the primary goal of exercise is to enhance my quality of life today and in the future. All the other benefits of exercise are great, but my health is my overidding concern. So sports related injuries would be counter to my primary concern of good health. That means my routine in the gym isn't full bore, balls to the wall maximum effort.
I've found that I tend to maintain forward progress best while minimizing injury (strains, etc.) by working with less weight in higher rep schemes. Occasionally I get the itch to go heavy, see where my 1RM is at, but that is an urge I find it much easier to quell these days.
A strained back can easily knock me out of the gym for a week or two and that is even more counterproductive to my goals than not being able to lift heavy and hard. I'm not going easy in the gym, but I don't feel the need to appeal to other people's egos, and my ego is founded upon the quality of my life and that is something I've learned to enjoy on my own.
Bottom line is I'm pretty happy with myself. I have goals but I'm satisfied that I'm working toward those goals and making measurable progress. Living the good life is what keeps me motivated.