I'm a second-year med student. Just got back from studying. Only 12 hours today, though!
Short version of what's below: yesterday was my birthday and my gift to myself was a set of ear plugs. Sounds exciting? Read on...
IMO, the best personality traits for succeeding in med school are competitiveness, tenacity and a fair measure of masochism (sit through 6hrs of lectures, then hammer notes into your head for another 6 - or until your eyes hurt - then repeat day-in, day-out without completely losing it requires one to take at least some pleasure in this sort of thing!).
These traits, along with average intelligence, will probably get you to where you want to be in medicine (I hope - at least for my sake). Sounds like a med student will succeed pretty much anywhere, right? I don't think so. I picked med school because I hate uncertainty. I'm terrible at motivating myself and I lack all initiative. How about $200k in loans for motivation? That'll make you put your ass in gear real fast!
Provided you put in the necessary hours, medicine offers the guarantee of an intellectually, morally, and financially rewarding career. A railroad track to success. How's that for motivation? Works for me. Yes, there do exist many options. But they are all relatively low-risk. You'll never be forced to starve with an MD (or DO).
If I had to do it all over again, I'd change two things: take more science classes in undergrad and get better grades in them. I took the basic required pre-med classes, got As and some Bs and indulged my interest in humanities with a bunch of GPA-padding BS classes. Totally not worth it. I didn't get in anywhere on the first try because I didn't play their game. Med schools put your application through the sieve of science grades and MCAT score; based on these factors they decide whether to offer you an interview or not. Having friends on the admission committee doesn't hurt either...
Despite being in the nadir of my social life during the prime of my youth, I'm excited about the future. In the end, if you work hard enough - if you're able to force yourself to work hard enough - things will work out. At least that's the thought that helps me sleep at night.