This is to illustrate how easy it is to overeat.
The left of the image above shows better choices, that are higher in protein, lower in carbs, will fill you up and still taste delicious.
The right of the image shows different choices you could make at each time you eat, which while at a glance is similar in volume, comes in at more than 1,100 calories more.
To put that in perspective, for every 3,500 calories that you overeat/don't use, you add a pound of fat.
1600 calories may not sound like much, and some people will need more, however the good quality, filling food on left will be enough for most people and should mean you don't ever feel hungry during an average day (ie. working in an office).
Now, the above is a very simplified approach, but if you're looking to lose weight, without sacrificing muscle, energy or focus, foods on the left-hand side and similar choices will help you to achieve that.
I'm always happy to answer any questions you may have about the specifics/nitty-gritty, so fire away!
Matt "yes but no apples for me please" Boyles
PS. I use an amazing free app called MyFitnessPal to track foods (when I need to - it doesn't have to be a daily process for you either)