Well yes, weight is mostly about calories in vs calories out. There are plenty of other things which affect weight, metabolism included, but they are far less significant factors than calorie intake and expenditure, particularly if we ignore bodybuilding and people at extreme ends of the BMI spectrum.
Losing weight is a challenge for us because we like routines and develop habits. When you're used to getting chips from the canteen for lunch, it can be hard to get into the habit of making sandwiches the night before, remembering to take them in, resisting buying chips as well as the butties, etc.
That's why diets often work for people - they provide instructional, demonstrable, evidenced weight loss techniques, even if they are effectively just trying to reduce calorie intake.
I'm in the process of losing weight, and since starting each month have either maintained or lost weight and reduced BF%. I'm purely doing it on having a flexible calorie limit. I eat whatever food item I want and just make sure not to go over my calorie limit more than a couple of times a week.