More subtle as in still not a healthy diet with exercise?

Let's take a pound of fat as 3500 calories. To gain one pound in a year is an average of 9.59 excess calories per day. Or about 0.5% of the typical total daily intake.

Yeah, managing a system within 0.5% is subtle.

Especially when biologically and psychologically the pressure is towards over consuming rather than under. If you consistently eat a deficit you will very obviously feel hungry. If you consistently eat a small excess the effects that would lead you to regulate are much more... subtle.

Judging from the downvotes my observation got, you're not the only person who skipped math class. I couldn't say it any better than the comment below this one that already replied to you. 10 calories a day, expressed in candy, is two M&Ms.