If you face the exact same problem 10 times, and you think it through from the beginning every single time, you're going to get 10 different answers. You just can't remember all the little details every single time.
Once in a while I surprise myself by independently coming up with exactly the same designs for similar problems (or, in fact, the same problem that I forgot I solved already few months ago). Most of the time I don't remember any details of the problem besides the general idea that I had it before. And then when I finally dig up the code it looks exactly like I was going to write (or was in the process of writing :)).
I think experience can actually become a liability. Things have changed and you don't have to write assembly code to optimize your program. Compilers will probably do a better job than you. And if you have a lot of experience writing JavaScript for IE6, you may actually be wasting time optimizing in ways no longer relevant.
True, but this is why you tend to migrate towards an architect/lead role later in your career where the general insights about systems and design are still applicable with out needing to overly focus on present day implementation minutia .
If you face the exact same problem 10 times, and you think it through from the beginning every single time, you're going to get 10 different answers. You just can't remember all the little details every single time.