Growing up with a single mother we've vacillated between being poor, broke and "getting by".
It was always a reverse slide down.
First, we'd go broke. The meager savings she'd put together would get wiped out. It was generally an impossible crisis that would do it. Something that shouldn't have broken, did. Something that shouldn't have happened, did. Something that should have only cost X cost Y.
If the crisis was a single instance event that year, we'd slowly return to "getting buy". Small savings would get restored. Some debt written off. A windfall from something or other that put our heads above water.
But sometimes, it was too many things at once. We'd go from being broke, to being poor. Every dollar was a trade-off. There was no "even" or "reduced". There was just "no". The water bill couldn't get paid. The mortgage had to be late. The credit card was going to default. There were no options to shave or save. The bare minimum was still too expensive.
The answer is just ... luck.
When you're broke, you're on borrowed time. For some people, at some point, that debt comes due and can never be repaid. For some people, the debt comes due but something balances it. For others, the debt just never gets called in.