All I Insist On Is That

The letter is preserved in Emily Anderson's The Letters of Mozart and His Family (1938), p. 1114, and in the Sadie/Smart edition (Springer, 2016), p. 749. The recipient and date are not conclusively established. The passage appears to be advice Mozart was giving — possibly to a younger musician — about the importance of courage in expressing oneself, choosing the right moment for speech but making that speech count when it comes. One website raised an unsubstantiated concern about forgery, but the scholarly editions treat it as authentic; the tone is consistent with Mozart's well-documented impatience with timidity and social performance.