'No one trusts a model except the man who wrote it; everyone trusts an observation, except the man who made it.' Harlow Shapley
I heard a variant of this saying (model=>theory, observation=>experiment) which was attributed to Einstein, but this one seems more common. I can't find the original source, though.
"A hypothesis or theory is clear, decisive, and positive, but it is believed by no one but the person who created it. Experimental findings, on the other hand, are messy, inexact things, which are believed by everyone except the person who did that work."
Harlow Shapley Through Rugged Ways to the Stars