The only way to have real success in science, the field I’m familiar with, is to describe the evidence very carefully without regard to the way you feel it should be. If you have a theory, you must try to explain what’s good and what’s bad about it equally. In science, you learn a kind of standard integrity and honesty.
Feynman argues that scientific reasoning requires evidence to be described as accurately as possible, even when it conflicts with a researcher’s expectations or preferred theory. A convincing idea should not be protected from inconvenient observations; its weaknesses and limitations should be examined alongside the evidence that supports it.
The quotation presents this practice as a form of intellectual integrity. Scientists are expected to resist selective reporting, wishful thinking and the temptation to emphasise only favourable results. By considering both what supports a theory and what counts against it, researchers make it easier for others to judge the strength of the claim. Feynman’s broader point is that scientific honesty depends on separating what the evidence shows from what a person hopes will be true. The principle also applies beyond science wherever beliefs or decisions need to be tested against contrary evidence.