Jeff talks a lot about this in his recent letter to shareholders. https://www.sec.gov/Archives/edgar/data/1018724/000119312518121161/d456916dex991.htm https://

Jeff talks a lot about this in his recent letter to shareholders. https://www.sec.gov/Archives/edgar/data/1018724/000119312518121161/d456916dex991.htm https://www.sec.gov/Archives/edgar/data/1018724/000119312518... He suggests that a great memo takes a week or more. In my experience that's roughly right, though you'll often have been mulling over the problem for weeks before you actually start writing.