I have commented before about careful site selection for a spot that will stay dry in rain. The site below, forecast was for a couple inches of rain overnight, so we were extra careful to pick a site that had good drainage, and this site had good drainage to a wetland that was to the left of the photo. The problem was that we had something like 6 or 7 inches of rain and several acres all drained to the same wetland, that wetland became a pond and did not drain by itself. The wetland is off to the left out of the photo, the tent was essentially on the shoreline of that pond which did not have a good outlet to flow to the lake.
Hung my sleeping bag on a clothesline the next morning, the steady stream of water flowing out of it is the whiteish gray line on the left side of the photo below the bag, I was really glad to have brought a synthetic bag instead of a down bag on this trip. Fortunately, our schedule was flexible so we could stay there that night and take the day to dry out.
Bottom line, we were careful, but not careful enough, I think the site would have been fine for the couple inches that was forecast but not the deluge. It was not enough in that case to make sure that your immediate site had good drainage.