I thought about this a lot when I was applying. Basically, I feel that I could be happy doing any number of things, including getting my PhD and working in academia. At this point in my life, it is more "why not?" than "why?" I really enjoy school, am good at it, and would love to spend more time learning and researching. Crucially, they're paying me. Sure, I'm missing out on other earning potential, but I'm not going into debt, so if I end up not using my PhD, so be it. I think that I will enjoy the experience enough to justify spending the next five/six/however many years of my life in grad school. I've started to become a little worried when I hear other students saying that you really need to know for sure that this is what you want to do, or that a PhD can make you overqualified for things, or that you'll get sucked into the idea that not finishing or not getting a TT job is a failure, even when you're not enjoying it anymore. For me, this was the most attractive of the options I thought about for my life, but not the ONLY place I could see myself. Is that not enough?