I usually feel better when I get milk in my diet. I suppose it's just because milk is a reasonably good source of protein, fat, and calories, and relatively easy to digest. (That is, if you aren't lactose-intolerant, which is fairly common especially in people whose ancestors didn't have domestic cows or goats.)
It's not milk specifically that makes things better, though. Just milk, meat, vegetables, fruit--you know, generally wholesome food.
It's when I end up eating the same thing over and over, or subsisting on junk that's easy to prepare, that I lose focus. I take vitamin supplements now to prevent nutritional deficiencies from being unable to feed myself a reasonably good diet, so that helps cover for at least some of the drawbacks, but it's still not the same thing as eating the actual foods.
I don't know how often I've wished for my meals to come in neat little boxes, everything pre-measured, so I wouldn't have to worry about preparing food or managing my diet. And no, those horrible TV dinners don't count; they're either nutrient-poor or too small, or both. (For example: 175 calories does not make a meal, however much "Healthy Choice" thinks it does.)