We’ve learned from experience that the truth will come out. Other experimenters will repeat your experiment and find out whether you were wrong or right. Nature’s phenomena will agree or they’ll disagree with your theory. And, although you may gain some temporary fame and excitement, you will not gain a good reputation as a scientist if you haven’t tried to be very careful in this kind of work.
Feynman argues that scientific claims are ultimately exposed to independent testing. Other researchers can repeat an experiment, and observations of nature can support or contradict a proposed theory. Because results are open to verification, misleading conclusions or careless methods may provide only temporary recognition before their weaknesses become apparent.
The quotation also links scientific reputation to intellectual honesty and methodological care. Feynman’s point is that a scientist should make a serious effort to identify possible errors, limitations and alternative explanations rather than presenting results more confidently than the evidence allows. Reproducibility and comparison with observation act as safeguards against individual mistakes or self-deception. The passage therefore presents scientific integrity not simply as a matter of personal virtue, but as a practical requirement of a system in which claims remain open to scrutiny and correction by evidence.