A great approach, too
in that the narrative manner isn't that of the dry declaration of facts and figures, but resembles what you'd get if you were with him and having a conversation. I've not read the Pepys diary but that's been described to me as very natural and unforced; I wonder if it's as good as Catalonia in this respect.
Orwell built a believable point of view as well, not pretending to knowledge he didn't have but clearly stating all he knew at one time, then amending his impressions only with experience or direct testimony from others. If he heard a rumor, he calls it a rumor. All this results in a flawless picture of the state of being in the trenches (literally) between the machinations of powers behind the scenes and an implacable enemy in front.