Because of the severely bad economic times we're in, many people are choosing to file chapter 7 bankruptcies themselves, without an attorney. For those who own virtually nothing and have little or no income, this might not be a bad idea if you take the time to research how to do this, such as reading the Nolo Press book, and if you are good at this sort of thing. Even in that case you might end up in trouble, though your chances of that are far less than someone with decent income and/or property.
Many people have the misconception that filing bankruptcy merely requires filling out some forms. While it is true that you have to fill out many forms, there's much more to a proper bankruptcy filing than that. Without having a good grasp of the bankruptcy laws, you risk losing a lot of money by doing the wrong thing. For example, a failure to exempt property properly could cost you that property. This is only one example of a really simple mistake; there are far too many possible mistakes to list here, and most of them are more complicated.
If you have very little or no income and cannot afford to pay a bankruptcy attorney but still feel that you must file bankruptcy, you have no choice but to file yourself. However, if this is your situation, you should check out whether you are "judgment proof" and, if so, ask yourself if you still want to file bankruptcy. If you have nothing a creditor could take, your income could not be garnished, and you own no real property and probably never will, you probably do not need to file bankruptcy.
If you have either decent income or some assets, you will be taking a big risk if you file bankruptcy on your own. Even if it's a financial strain, paying a competent attorney to file your bankruptcy could save you much more than you pay.