“When Dirac was an old man, younger physicists often asked him how he felt when he discovered the [Dirac] equation. From his replies, it seems that he alternated between ecstasy and fear: although elated to have solved his problem so neatly, he worried that he would be the latest victim of the 'great tragedy of science' described in 1870 by Thomas Huxley; 'the slaying of a beautiful theory by an ugly fact'. Dirac later confessed that his dread of such an outcome was so intense that he was 'too scared' to use it to make detailed predictions of the energy levels of atomic hydrogen - a test that he knew it had to pass. He did an approximate version of the calculation and showed that there was acceptable agreement but did not go on to risk failure by subjecting his theory to a more rigorous examination.”