This certainly applies to programming but I've felt it too in my Aerospace career. I used to feel like the smartest guy, I always knew how to do things or learnt them really fast, and I couldn't imagine where the horizon was. Now, the more I see, the further I feel the horizon is, and it's pretty frustrating as it makes me feel less intelligent.

Your comparison helped me to see things a bit clearer and to be a bit more motivated.