Who Turned Out the Lights?

Why is it that when one lightbulb goes out, suddenly you look around and notice that half of the bulbs in your house need replacing? And of course, when you head out to check on your lightbulb stash in the garage, you discover that you've already used all your spares, so it's off to Target. And when did lightbulbs get so expensive? I can't believe it cost me $50 just to keep my lights going. I think in the future I need to buy a sleeve a bulbs once a month with the groceries so that I don't go into sticker shock again. Having to replace 20+ bulbs all at the same time is just way too expensive!