By honest I don’t mean that you only tell what’s true. But you make clear the entire situation. You make clear all the information that is required for somebody else who is intelligent to make up their mind.
Feynman argues that honesty requires more than avoiding statements that are literally false. A person can still mislead by leaving out important qualifications, conflicting evidence or relevant uncertainties. Genuine transparency means presenting enough of the surrounding information for others to understand the situation rather than steering them towards a preferred conclusion.
The quotation reflects Feynman’s wider view of scientific integrity. Researchers should disclose evidence that weakens their case as well as evidence that supports it, allowing other people to evaluate the argument independently. The principle therefore treats honesty as a standard of completeness as well as accuracy. It applies beyond science wherever decisions depend on evidence: responsible communication should provide the context, limitations and material facts needed for an informed judgement rather than merely presenting statements that are technically true.