Talent and genius operate outside the rules, and theory conflicts with practice.
– Carl von Clausewitz, 1780 – 1831

One of the most difficult features of direct experience is that it is unfiltered by any theories or expectations. It’s hard to observe without imposing a theory to explain what we’re seeing, but the trouble with theories, as Einstein said, is that they explain not only what is observed, but what can be observed. We start to build expectations based on our theories.
– Michael Crichton, 1942 – 2008

Modern psychology teaches that experience is not merely the best teacher, but the only possible teacher.. There is no war between theory and practice. The most valuable experience demands both, and the theory should supplement the practice and not precede it.
– Charles F. Kettering, 1876 – 1958

In theory, there is no difference between theory and practice. But, in practice, there is.
– Jan L. A. van de Snepscheut, 1953 – 1994

We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. My own feeling is that it is not crazy enough.
– Niels Bohr, 1885 – 1962