On Cost

Everything has a cost. Period. I really really REEEEEEEEALLY hate to admit it, but it does. I guess this means I have to work or something.
First, there are the obvious costs, like what you have to spend in order to obtain food, a house, a trained sloth, and so forth. These ones are straightforward. In order to eat for 2 days, I need to spend $xx.xx on food. Say you have twenty dollars. This will buy you food and drink for two days. This is the only money you have to do ANYTHING with at all.
You get bored and decide to alleviate your boredom with a good jog. That doesnt cost anything, right? You go out and do your jog. An hour later, you get back, and decide that you're thirsty. You reach into your refridgerator and pull out some water, and drink it.
You've just gone into your water stash. By jogging, you have increased the needs of your body (water) such that you had to drink more water to make up for it. In doing so, you will have to go buy more water to make up for the water that you just drank. Aha, a hidden cost.
Costs arent just monetary. Theres the much bigger issue of time. By doing one thing, you lose the opportunity to do other things. When you go jogging, you lose that block of time. You cannot use it to read, or go swimming, or play WoW. Time is a cost too, one larger than money.