And as we devote resources to environmental protection, it's important to remember the law of diminishing returns. For instance, think about cleaning your house. At first, there are noticeable gains from picking up, vacuuming and dusting. At a point, though, the cost of effort in cleaning isn't worth the benefit you'll receive. You're not about to move the fridge every day to get the dust and crumbs in the back corner of your kitchen.