Everything should be made as simple as possible, but not simpler

I came across this quote, attributed, of course, to Einstein.

Everything should be made as simple as possible, but not simpler.

From a forecasting and modeling perspective it is perfect because it is true. But did he say it.

The genealogy of the quotation is traced by Garson O’Toole in his sterling website, Quote Investigator. No, Einstein did not quite say this. The likely inspiration was this quotation from “On the Method of Theoretical Physics,” the Herbert Spencer Lecture, Oxford, June 10, 1933 published by the Oxford University’ Press.

It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience.

Close, but the vernacular version is pithier. Or perhaps it might be better characterized as simpler but not too simple.