Quotations about the power of simple ideas I'm looking for quotations about how very simple mathematical ideas can be very powerful. I know of a few, but they're not quite what I'm looking for insofar as they contain criticism of other mathematicians, and I'm looking for quotations that are more unambiguously affirmative. 
Two that are in the direction of what I'm looking for are:


*

*The very notion of a scheme has a child-like simplicity - so simple, so humble in fact that no one before me had the audacity to take it seriously. So ”infantile” in fact, that for many years afterwards, and in spite of all the evidence, for so many of my ”learned” colleagues, it was treated as a triviality. – Alexander Grothendieck 

*It is the snobbishness of the young to suppose that a theorem is trivial because the proof  is trivial. – John Whitehead 
Any better examples?
 A: Imaginary numbers appear in algebra when we try to take square roots
of negative numbers.... Geometric interpretation consists in observing that
two consecutive rotations of the plane by 90 degrees around a fixed point
reverse the directions of the vectors. If we think of the 180-degree
rotation reversing vectors as the geometric counterpart of multiplication
of numbers by -1 reversing the sign, then we are inclined to accept the
90-degree rotation (of the plane containing the line of real numbers)
as the square root of -1.
 All this looks childlishly simple, why do mathematicians make such a fuss
around it? How can one dare to compare this plain idea to profound
philosophical pronouncements, such as "Cogito ergo sum" of Descartes?
But look (as my colleague David Ruelle once suggested) from another perspective.
"Cogito ergo sum" stayed unperturbed for more than three centuries,
like a monument, a Greek statue, a magnificent piece of art, impervious
to the flow of time, whilst the little speck of dust, the square root of -1,
have been growing and developing for hundreds of years in the minds of
mathematicians, geniuses like Cauchy, Gauss and Riemann, and turned into an evergreen intensely alive vibrant tree supporting in its branches our
sacred knowledge - quantum mechanics - ruling everything we see (and do not see)
in this world.
(Misha Gromov, Local and global in geometry, October 29, 1999.)
A: Atle Selberg (Interview, June 11, 1989, page 30):

In some sense, I think those are probably the most important things, those that can be made simple.

Or, with one more phrase of context.

There are other things in mathematics that may seem impossible to begin with, but after they have been done they seem very simple. In some sense, I think those are probably the most important things, those that can be made simple. 

A: Here is a quote from The Power of Mathematics by John Conway.  

What I like doing is taking something
  that other people thought was
  complicated and difficult to
  understand, and finding a simple idea,
  so that any fool – and, in this case,
  you – can understand the complicated
  thing. These simple ideas can be
  astonishingly powerful, and they are
  also astonishingly difficult to find.
  Many times it has taken a century or
  more for someone to have the simple
  idea; in fact it has often taken two
  thousand years, because often the
  Greeks could have had that idea, and
  they didn’t. People often have the
  misconception that what someone like
  Einstein did is complicated. No, the
  truly earthshattering ideas are simple
  ones. But these ideas often have a
  subtlety of some sort, which stops
  people from thinking of them. The
  simple idea involves a question nobody
  had thought of asking.

