That wasn’t true for me personally. I personally lost weight almost with mechanical precision. About a 7500 calorie deficit resulted indeed in 1 lost kg. That’s with about half the deficit coming from exercise and the other half coming from cutting calories and is using all the bog-standard formulas for roughly estimating my base metabolism. I was astonished by the mechanical precision of those number, really astonished. I didn’t expect that at all.
However, this has many moving parts and cheating (mostly by consuming more calories) is ridiculously easy. My guess would be that that’s the effect many people see when they don’t succeed. All of this is really hard and I was lucky to be in an extremely privileged position where I could devote lots of my attention to this task. Not many people are so lucky. Motivation obviously plays a crucial role and I absolutely do believe that it is central to successfully losing weight. The mechanics are simple and do indeed work like clockwork. But that doesn’t mean you can make them work like clockwork for yourself …
So, yeah, the body may be astonishingly mechanical when you execute everything perfectly, but motivation is the crucial second parts that allows you to execute everything correctly. And it may well be that to keep motivated it helps to be active or to eat certain thing. (I, for example, know that eating pasta with tomato sauce – formerly my absolute favourite food – will keep me hungry for longer. Meanwhile the same amount of calories from some salad with a vinaigrette and grilled chicken breast will keep me feeling full for longer.)