Max Born and Albert Einstein disagreed about how to interpret quantum mechanics, and they argued about it in print. Born commented on this when their letters were published in German in 1969. Auch diese im Druck niedergelegte Meinungsverschiedenheit hat die Freundschaft zwischen uns nicht im leisesten gestört. This difference of opinion, too, set down in print, did not disturb the friendship between us in the least. He added that Einstein had explicitly acknowledged the warm tone of his article.