Oddly, this does not end up true for dieting, as I've found out. I dieted, lost a lot of weight with a prescription pill and then more on Weight Watchers. I thought I knew what I was doing, and could "count calories" without actually tracking them.

What I found was that I might know certain things that I eat often, but anything even a little new ended up being badly estimated. If I want to continue losing weight, I need to track.

And my estimates went both ways, too. I discovered this one day when I was crazy hungry, and it turned out I'd massively under-eaten that day (or the day before? I forget), which can be as bad for dieting as over-eating thanks to the lowered metabolism and then compensatory over-eating that eventually happens.