Do write, but also measure the exact amounts of foods you put on your plate. It's shocking how we underestimate how much we eat when we try to measure it at a glance. I used MyFitnessPal for nearly a year, and for the most part, I also looked at exactly how much I was eating. Extreme? Maybe. But if you don't do that, and only assume, it's like pouring oil with the bottle on your salad and swearing you've only "poured" just one tablespoon :D