Most days I can push myself to perform at demanding levels without the assistance of a group to urge me on. In fact, most of the time I have to be careful that I don't over-train. Since I am über competitive by nature, Crossfit and I would not be a great fit, because that environment would make me push too hard, and I know from past experience that's how one gets injured.
Oddly (for a fat, non-athletic, academic 63 year old woman) I am the same way. I seem to have taken to lifting really well, but the down side is that now that I am feeling more successful I find I get pretty competitive if I don't watch out. I try really hard to compete with myself only, but still, it is hard not to notice what others are lifting at the gym.
Also, I could probably lift maybe 50% heavier weights if I wanted to, once, but my form would get a lot worse if I did and I would probably get injured. Still, I am lifting about 3 times as much I lifted a year ago when I started, by attending consistently and slowly, sanely increasing, and I feel very accomplished relative to my starting level of complete and utter non-fitness. That sense of accomplishment motives me to continue. Good enough for me.
Oh, and by the way I had a routine doctor's appointment on Dec 28th, and my doctor is very happy with the effects of lifting on my overall health. I still need to lose lots of weight, but apparently I am doing fine on the exercise front.
I haven't been doing much if any cardio and should probably add some, but meanwhile reasonably prompt, not-quite-brisk lifting seems to be helping on that front.
And there are things I see done in Crossfit boxes that make me cringe in fear of seeing someone getting hurt. Kipping pull-ups for example.
I had no idea what a kipping pull-up might be, so I just looked it up on youtube. Those people are CRAZY, IMHO!!
At least for me, it would be because that kind of activity would pull my arms almost out of their sockets.