They avoid debt by avoiding debt, living day-to-day within ones means. For poor people, the trick is to save up for everything. No college loans. Live in someone's basement for lower rent then move up to the most modest choice. Public transportation, walk, or bicycle. Budget the spending money for an interval and stay within it. Have a credit card, but for things you've already saved the money for. Keep the utilities and technology at the minimum needed to function. Public libraries. Buy clothing sensibly so it doesn't go out of style or fall apart. etc
I call it living "upper poor". Once one gets ahead of the game when younger, it's possible to accumulate some savings even on low incomes.
I think I wrote wrong; why is it that someone with a fat paycheck ends up to debt in their eyeballs? All that cash coming in and yet the maroons end up filling for bankruptcy.