The only simplicity for which I would give a straw is that which is on the other side of the complex — not that which never has divined it.

Oliver Wendell Holmes, Jr. (1841–1935) American jurist, Supreme Court Justice

Letter (1902-10-24) to Lady Georgina Deffell Pollock
    (Source)

In context, criticizing those who praise simplicity (at least in literature, if not beyond), except that simplicity which results after a synthesis of the complex.

Collected in Mark Howe (ed.), Holmes-Pollock Letters: The Correspondence of Mr. Justice Holmes and Sir Frederick Pollock, 1874-1932 (1961).

This quotation is frequently misattributed to his father, Oliver Wendell Holmes, Sr. It also has (at least two) incorrect variants that are seen more frequently on the Internet:

For the simplicity on this side of complexity, I wouldn't give you a fig. But for the simplicity on the other side of complexity, for that I would give you anything I have.

I wouldn’t give a fig for the simplicity on this side of complexity; I would give my right arm for the simplicity on the far side of complexity.