If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is.
John Louis von Neumann

Chess, like mathematics and music, is a nursery for child prodigies.

Jamie Murphy

Consequently he who wishes to attain to human perfection, must therefore first study Logic, next the various branches of Mathematics in their proper order, then Physics, and lastly Metaphysics.

Maimonides

Everyone knows what a curve is, until he has studied enough mathematics to become confused through the countless number of possible exceptions.

Felix Klein

As far as the laws of mathematics refer to reality, they are not certain, and as far as they are certain, they do not refer to reality.

Albert Einstein

One reason why mathematics enjoys special esteem, above all other sciences, is that its propositions are absolutely certain and indisputable, ... How can it be that mathematics, being after all a product of human thought which is independent of experience, is so admirably appropriate to the objects of reality.
Albert Einstein

 Mathematics is not a deductive science -- that's a cliche. When you try to prove a theorem, you don't just list the hypotheses, and then start to reason. What you do is trial and error, experimentation, guesswork.

Paul R. Halmos, in I Want to be a Mathematician, Washington: MAA Spectrum, 1985.

“Arithmetic is numbers you squeeze from your head to your hand to your pencil to your paper till you get the answer.”

“Mathematics is made of 50 percent formulas, 50 percent proofs, and 50 percent imagination.”

"One cannot really argue with a mathematical theorem."

"Mathematics is the science of definiteness, the necessary vocabulary of those who know."

W. J. White

"The mathematician does not study pure mathematics because it is useful; he studies it 

because he delights in it and he delights in it because it is beautiful."  

Henri Poincare