I realize that. No phone that is turned on and connected to the network (or wi-fi) is probably ever actually "doing nothing", so maybe my phrasing it that way was oversimplifying. What I was getting at is that the screen isn't on (which is probably the biggest battery eater) and activity is minimal compared to when it's being actively used during the day for phone calls, texts, web browsing, gaming, etc.
My point was just that it would seem unusual, at least to me, to lose 10% battery while sitting on the nightstand overnight. I could maybe see it happening if somebody had a ton of background tasks running, but if I ever lost 10% overnight I'd be digging into settings and seeing what's causing it because I've never seen it before on any of my iPhones and I wouldn't consider it normal.