I highly recommend people get a food scale/measuring cups and weighing everything single thing they eat (even small things like nuts and cooking oil) for at least two weeks. After that I think you have a much better appreciation for how many calories your regular meals and snacks have.
+1
The killer for me was breakfast cereals. The box shows a full bowl of whatever, full to the brim etc. in reality the pictures are probably 5 or 6 or more servings - a single serving would barely even cover the base of the bowl and even then be 200ish calories before milk.
If you just pour yourself "a bowl" of cereal without thinking or weighing then you're probably having 1200+ calories (or about 50% of your entire daily quota) even before you add milk or anything else, just for breakfast.
I counted calories and put everything on a scale, for about 2 or 3 months in 2022 (iirc). And you are 100% right. I had absolutely no idea how much calories some food has. There were a lot of things, but I think cashews were my biggest eye opener (probably obvious to a lot of people). I easily achieved my goal of -10kg and saved A LOT of money, because I always had food prepared. And since I was going for a calorie deficit, I easily could afford a few sweets on the weekend.
Then I obviously got lazy. And while I sometimes still think I can estimate how much I am eating, I am probably wrong, because my bathroom scale says something different. My key takeaway is that it takes quite a bit of effort, but once you got into a routine, it's not hard.
Edit: Also, while I might have tried to ditch "wasted calories", I didn't put too much effort in eating healthy. One step at a time.