CICO is one of the few things in nutrition which is 100% fact: if you’re not losing weight after months, you’re eating too much, and if you eat less, you will lose weight.
But CICO alone is terrible nutrition advice, because hunger - true physical hunger - is not something anyone should live with. Those people in the Minnesota Starvation experiment? They were thinking about food 24/7, obsessing about it, it became nearly the only thing they cared about. One of them reported when watching a movie, he would pay most attention to the few scenes with the characters eating, not the action or romance or the actual plot. Furthermore, your body really does have sort of “starvation mode”: it won’t lower your RMR to 0, but it will cause brain fog, tiredness, loss of sex drive, mood dysregulation, and ultimately depression. You stop getting pleasure from anything except food.
Furthermore, you can get “physical hunger” even if you’re gaining weight, if your hormones are messed up. A cited example is hypothyroidism, which has symptoms like brain fog, fatigue, mood disorders synonymous with starvation. And you can avoid “physical hunger” even while losing weight, if your hormones are in check, you’re not in too steep a calorie deficit, and you’re getting enough nutrients (aka eating whole foods). This is why people emphasize eating nutritious foods even when you can reach the same calorie goal with junk foods.
There’s also the willpower component. Nutritious foods can improve your mood and give you more willpower, so it’s easier to eat less. They also tend to make people less (mentally) hungry. Generally when losing weight it’s a good idea to not just focus on nutrient-dense “whole” foods, but also low-volume and satiety-inducing foods. Nuts and whole grains are generally considered healthy but they’re also calorie-dense so it’s easy to pass your daily calorie needs them without getting full: in contrast, lean proteins and non-starchy vegetables are low-calorie and filling, it’s much harder to gain weight on fish and broccoli. Eating in a smaller time window and eating less meals (IF) also makes it easier to not overeat.
But even with IF, volume eating, and sometimes keto, you can still deal with physical hunger if your hormones are just messed up. To see if it’s your hormones first you need to stick to a consistent diet for at least a couple weeks: you will probably feel hungry and tired the first few days of any diet but that’s just your body adapting. After a few weeks if you’re “doing everything right”, including eating truly “healthy” foods (whole foods), eating low-calorie foods, and eating a moderate but not too steep deficit from your estimated TDEE; if you’re doing all that and either you’re not losing weight or your still white-knuckling it and getting symptoms like tiredness and hair loss, you should see a doctor and get your hormones checked.