He who truly knows, knows that he knows not

Or

The more you know, the more you realize you don’t know.

But also, understanding that about yourself doesn’t take more knowledge or intelligence than you currently have. As another user (darkdarkhouse)^ posted, you can understand how the brain works and still not have all the knowledge in the world (hard drive with a map/directory of the hard drive on it).

My duck: waterproof feathers

Yo duck: named something like Heather

My duck: green ring mallard.
Yo duck: tastes good in salad

My duck: super sized.
Yo duck: look like two fries.