Well it is generally a person's fault because they live in poverty. Even when they work "several" jobs they are all low/no skill jobs which they are generally overpaid to work.
There are also a ridiculous number of social programs that will give the "poor" free food and money for nothing in order to help them "pay for things"
You see, the fallacy there is that it assumes the outcome is only dependent on the person's own actions, and nothing else - which is nonsense, of course. Among other things, that mentality ignores the circumstances the person is in, as TaunSew's post alluded to, but it also ignores the environment that person grew up in and the opportunities it was afforded. I mean, just look at the studies for social mobility in developed countries and see how the US is doing.