Men who have excessive faith in their theories or ideas are not only ill prepared for making discoveries; they also make very poor observations. Of necessity, they observe with a preconceived idea, and when they devise an experiment, they can see, in its results,only a confirmation of their theory. In this way they distort observation and often neglect very important facts because they do not further their aim.

Claude Bernard (1813 CE-1878 CE), Claude Bernard was a French physiologist. Bernard Cohen of Harvard University called Bernard "one of the greatest of all men of science". He originated the term milieu intérieur and the associated concept of homeostasis (the latter term being coined by Walter Cannon)