I don't know I think it depends on the person. I am the living proof that you can lose weight without even owning a scale.
You have to be very honest with yourself though. Even without seeing it in numbers, of course you have to watch yourself and not eat crap/too much

And it IS really hard not to eat too much of certain foods... chocholate is my downfall. Some foods - and especially the very very good ones it seems - are just so calorie dense, that there is almost no way of not eating too much.