You're on the streets, have no food, it's cold, raining, dark and you're wet. This is the 10th day. I offer you something to make it all go away for a couple of hours. Maybe you deny this time. But two weeks later you're more broken than ever, and you start shooting that Heroin or smoking that Crack. Just to make it go away for a short time.

When you have nothing else to live for you are more likely to turn to such escapes. The correlation is pretty strong, even though it isn't a strict cause-effect relation.

Yes of course people who own a house do drugs. Some of them destroy their mind to the point they can no longer keep their house.

The simplest hypothesis is that drug use and mental health lead to homelessness. And if that's the case, then the problem isn't housing costs (though high housing costs are a problem, just a separate one), it's that people have addiction and mental health issues.

The problem with your simple hypothesis is that the data doesn't back it up. Drugs & alcohol account for 15% of the reasons for homelessness in SF, and medical issues/illness account for 7%[1]. The data shows that housing costs and financial instability are the largest causes of homelessness in SF.

[1] http://hsh.sfgov.org/wp-content/uploads/2017/06/2017SanFranc...

Sorry, I should have been more specific: I am referring to visible homelessness, people living on the street, etc. The colloquial meaning of the term 'homeless', in other words. I should have been more specific, especially given that this confusion regarding the use of this term is a pet peeve of mine.

No problem, thanks for the clarification. It's a pet peeve of mine, as well.

When you're homeless, you don't have your own private bathroom.