Make room for ignorance: Unknown unknowns.

 "A library should include as much of what you do not know as your means allow". Quoted here.
This is in the same spirit as the Feynman quote heading this blog:  "Science is the belief in the ignorance of experts.".    At the link is another pointed quotation:  

“It is our knowledge — the things we are sure of — that makes the world go wrong and keeps us from seeing and learning.”  — Lincoln Steffens

To add one more layer to this ham sandwich before you bite down, remember Donald Rumsfeld's apothegm:  

"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones".