I originally started monitoring my calorie intake to make sure I was eating enough, not for weight loss, but I now have a daily record of weight, calorie intake and exercise going back 22 years, and my experience is that reducing calories alone doesn't work.
The effect of eating less just seems to be that your body tries to adapt to the lower calorie intake and you feel cold and fatigued, whereas exercise teaches your body that it needs to maintain your metabolic rate and burn fat to make up the deficit. It seems entirely reasonable to me that evolution would produce a system that prioritises conserving fat over muscle in a famine victim who does no exercise. After I quit cycle touring I cut my calorie intake accordingly, and a year later my weight was still the same as it had been when I quit, but my chest had gone from looking like a xylophone to my ribs being covered by a thick layer of fat. On an occasion when I did need to lose weight, reducing calories alone repeatedly failed, I lost the weight by first increasing my exercise without increasing calories, then reducing calories as I returned my exercise back to where it had been.