To Play A Wrong Note Is

No verified primary source has been found for this exact phrasing. The sentiment closely echoes an account by Beethoven's pupil Ferdinand Ries, who wrote that Beethoven would forgive mistakes of execution but not failures of feeling or character: "Mistakes of the other kind, he said were due to chance; but these last resulted from want of knowledge, feeling or attention." The popular quote may be a later condensation of Ries's firsthand description.