This is a pretty important point. You can get a very small apartment in Austin, TX, for $500 (and many other non-SF cites). If you're able to, spending ~$16 a day versus living in a van makes a lot of sense. Completely different if you don't have that $16.
Landlords very often just won't take you on at all if you don't show evidence of preëxisting stability. No proof of stable income? No housing—you can even offer to pay up-front or whatever, and they just won't bother dealing with you as a special case, because why would they deal with the special case when there's a dozen other safe, predictable, normal people in line behind you?
Got an income, but can't prove it to be consistently enough? Congratulations, no housing for you. And thus begins the downward spiral.
Yep. I have bad personal credit (< 600) due to a cash-strapped entrepreneurial background and a strategic default, and it took over 10+ apartment tours before we found someone willing to rent to us--at any price, and with any amount of up-front deposit--once the credit check came back.
I doubt most of the folk we dealt with would have taken us on even if I had offered to pay a full year's rent up front. It's just not worth the bother when there's a dual-income, no-kids couple with good credit next in line.