As a successfully graduated grad student, I disagree. It is possible, but not at all easy, healthy or sustainable.
I've never seen anyone fail at it?
Fail at being a grad student? Tons of folks do. Grad degrees have a fairly low success rate and living conditions are certainly one of the reasons people drop out or leave early (the case where the student goes for a PhD and leaves after getting a masters). I'm not claiming it's the only reason, but it's certainly on the list.
As a 40-something person, I couldn't possibly live in the rathole I lived in when I was 20-something.