Reddit, why are you living paycheck to paycheck?

While reading a thread last week about how credit card companies don't charge your card chronologically, I noticed some heated discussion about being able to live within your means. I'm only 23, and I have zero debt, so I don't know what it takes to get into a situation where you just can't pay all the bills.

So, reddit, someone enlighten me. Why do you have to choose between electricity or gas this month? I wanna know about your plight, and maybe you can pass on some words of wisdom so that it never happens to anyone else.