Why do Calories Count?

We have all heard about counting calories and the recommended intake of 2,000 calories, but what exactly is a calorie? Technically, a Calorie is the amount of heat required to raise one mL of water, one degree Celsius. But, what does that mean for us in terms of nutrition? Basically, a calorie is a unit of energy (only energy could raise temperature).
You will notice that in the above paragraph I capitalized one Calorie and left the other uncapitalized (is that even a word?). When we are discussing food calories (not capitalized), the number on the nutrition label is technically a kilocalorie (1,000 normal Calories). Basically, a calorie is stored energy.
In chemistry, stored energy is also known as potential energy--it has the potential to do something. That is the same with calories in food, it has the potential to be energy!