How do people afford to live in SAN FRANCISCO ?

some may know what a HUGE fan i am of san fran. but i was checking out some links here http://sanfrancisco.lovetoknow.com/wiki/San_Francisco_Apartments and just wonder HOW to people afford to live there? i mean yes it is the dreamiest city ever but wow. do people have to have roomates etc. or do some have really great jobs. i am honestly curious.