I feel like a big thing is that people handle stress differently. You also usually never know what's going on in someone's head or when they're alone unless you're really close with them. Many people project an air of being confident and on top of their game at all times, but inside they're suffering from anxiety and self-doubt. Or the people who punish themselves for getting a B instead of an A, or HP instead of H. Internally they may be quite unhappy, but they appear less negative externally. I agree with
@Planes2Doc that there are definitely people who are completely miserable, but I think the majority of people just tolerate it and get through it.
It also has to do with your perspective. If you're a constant "glass half empty" person, everything is going to be a problem. There are definitely people who complain about EVERYTHING, and that can influence your own mentality if you let it. I've certainly done my fair share of complaining, as it's not all fun and games every day, but in general I try not to let that influence my perspective. Of course there were some very sucky times in MS1-MS2. And I know the worst of MS3 is yet to come. But overall big picture, it hasn't been completely miserable.
Didn't realize you were an MS2, I thought you were an MS3!! Yeah, pre-clinical years suck. A lot. And it all culminates in the absolute misery of Step 1. I agree with
@mimelim that you'll probably be one of the ones who really enjoys the clinical years. It's a different kind of stress level and different kind of difficulty, but I feel like I'm thriving in clerkships. We still have exams, but the majority of our grade is dependent on evaluations (which can be a good thing or a bad thing, depending on your attendings). You still get your butt kicked,
I've already had an attending make me cry (once I got to my car at the end of the day), but it's overall much more enjoyable. Just keep trucking through this year, and there's a light at the end of the tunnel.
Med school does hit people pretty hard, some more than others. I believe about 1/3 of our student body goes to see the (free and confidential) psychologist at some point. That's not to say that 1/3 are suffering from depression or pathologic anxiety, but everyone gets overwhelmed at times and it's good to have someone to talk to, especially someone who has been doing the job for years and has seen many classes go through the same exact things. But yes, the statistics about depression and SI among medical students are very real and apparent.