The principle of limited sloppiness

From Avoid Boring People, the autobiography of James D. Watson. Page 91.

3. Irreproducible results can be blessings in disguise

A desired result in science is gratifying, but there is no contentment until you have repeated your experiments several times and got the same answer. Al Hersehy called such moments of satisfaction "Hershey heaven." Just the opposite feeling of maddening inferno comes from irreproducible results. Albert Kelner and Renato Dulbecco felt it before they found that visible light can reverse much UV damage. Delbruck, struck by how long this phenomenon remained undiscovered, put it down to fastidiousness. He described what he called "the principle of limited sloppiness." If you are too sloppy, of course you never get reproducible results. But if you are just a little sloppy, you have a good chance of introducing an unsuspected variable and possibly nailing down an important new phenomenon. In contrast, always doing an experiment in precisely the same way limits you to exploring conditions that you already suspect might influence your experimental results. Before the Kelner-Dulbecco observations, no one had cause to suspect that under any conditions visible light could reverse the effects of UV irradiation. Great inspirations are often accidents.