How Some of the Great Composers Experienced Their Own Writings...

In the thirty odd years that Haydn was employed by the powerful Esterhazy family, the great composer would, from time to time, spend many of his mornings at the keyboard, improvising musical designs as they appeared on the blackboard of his mind. On countless occasions this giant, who wore the same uniform as the servants, would stop his extemporizing long enough to write out a design he particularly liked, and it is known that many of these ideas, which appeared like dew in his mind's eye/ear as he improvised, re-appeared at a later time in many of his compositions. What I cannot answer is which of these ideas we see on paper were born out of those mornings at the keyboard. Other composers may well have undergone the same process, but Haydn underwent this experience through much of those thirty years.
And what about Mozart? Astounding to me is that as many as five different compositions lay strewn out on his pool table, along with, I presume, an occasional bottle of wine. And it is known that this blindingly gifted genius was able to work on five different works, all within the time period he would give to these works, that morning, or afternoon, or evening. No other composer I know of could do such a thing.
And Brahms? Why did he destroy a number of works he did that displeased him? Any musicologist would extract an eye-tooth to see those works - I know that THIS student of musicology would!
Man IS Mystery... I utter this statement veritably every time I shave that image I see glaring at me in the mirror.