"What gets us into trouble is not what we don't know.
It's what we know for sure that just aint so."
- Yogi Berra/Mark Twain (I've heard attributions to both)
This is a great one. Think it through.
"...when you have eliminated the impossible, whatever remains,
however improbable, must be the truth."
- Sherlock Holmes, in Sign of Four by Sir Arthur Conan Doyle
Yes, he really does say this, though it is usually taken somewhat out of context. This phrase is embedded in a longer diatribe directed at Watson's failure to see what Holmes considers obvious.
"All we know so far is what doesn't work."
- Richard Feynman
And of course if you find something that does work, people will say "surely you must be joking."
"When we think we know, we cease to learn."
- Dr. Radhakrishnan
All of us are guilty of this sometimes, some of us are guilty of it all the time.
"Faced with the choice between changing one's mind and proving that there
is no need to do so, almost everybody gets busy on the proof."
J. K. Galbraith
Hence the persistence of such foolishness as Intelligent Design and any number of ApJ papers trying to fudge data in favor of NFW.
"My heart was beating faster; I was moved, trembling and
fascinated in the face of such mastery and refinement of beauty."
- Itchiku Kubota describing his reaction upon seeing an ancient piece of Tsujigahana fabric.
I felt much the same when I saw his magnificent kimono art.
"I've never observed wisdom to emerge from shouting."
- me, from long experience watching (and being involved in) heated debates.
"I'm sure it was a great honor for you to introduce me."
- Alan Sandage
A classic case of politeness gone ambiguous.
"Yes, I wrote papers on Cold Dark Matter, but I didn't inhale."
- John Peacock, to Carlos Frenk
Just like Clinton didn't.
The Frenk Principle:
"If the Cold Dark Matter Model does not agree
with observations, there must be physical processes, no matter how bizarre
or unlikely, that can explain the discrepancy."
I have heard two versions of the Strong Frenk Principle:
1: "The physical processes must be the most bizarre and unlikely..."
2: "If we are incapable of finding any physical processes to explain the discrepancy between CDM models and observations, then observations are wrong."
- George Efstathiou
This pretty much sums up the state of modern cosmology.
Link to similar quotes from a Princeton cosmology meeting of the same era.