The Seven Pillars of Statistical Wisdom book by
Stephen M. Stigler:
William Stanley Jevons, writing in his Principles of Science in 1874:
One of the most requisite precautions in experimentation is to vary only one circumstance at a time, and to maintain all other circumstances rigidly unchanged.
Ronald A. Fisher, writing in 1926:
No aphorism is more frequently repeated in connection with field trials, than that we must ask Nature few questions, or, ideally, one question, at a time. The writer [Fisher] is convinced that this view is wholly mistaken. Nature, he suggests, will best respond to a logical and carefully thought out questionnaire; indeed, if we ask her a single question, she will often refuse to answer until some other topic has been discussed.
I continued to finish the book and yet can't understand, what was the insight
When googling for an answer it seems the former idea (keep everything fixed and change one thing aka ceteris paribus) is the recommended approach.
What is the insight Fisher is talking about?