"Most commentaries in chess magazines and books are superficial and sometimes just awful. Once a certain experienced master explained to me how he worked. You put two fingers to the page with text on it and see that there are only moves under them - in other words, it is time to make a comment.
GM Barcza was helping GM Szabo prepare for a candidates' tournament. They were working on a particular line but couldn't figure it all out. Barcza finally said, "It must be tried out! And let the better player win!" Szabo cried out, "That is exactly what I do not want to happen!"