I have (compared to a lot of people I meet in this industry) a small brain. I don't have a PhD, I didn't do well in my degree, and I don't grok a lot of stuff immediately. I'm not suggesting that's in any way unusual, it's just something that's been on my mind lately.
I'm actually learning much more computer science stuff since graduating than I ever learned while at University. I think I was just too young while I was there - I was far more interested in sleeping late, and "spiritual growth". Now I actually find it fun learning things from the Dragon book about eliminating left recursion, and other things like that. Well OK, perhaps not fun. But at least I actually understand what I'm reading now, rather than hardly taking it all in.
Right now I'm trying to learn about Bayesian Probability. I seem to vaguely recall something about that at Uni, but it was over my head then. It's still over my head now - lots of maths. But hopefully I'll actually stick it out this time around.