While on one side the 3x rent rule might be just "good sense", most places won't consider you if your salary (or the salary of all tenants) isn't 3x your rent.
That seems to be one of the common and very popular requirements to even have your lease application put aside for consideration, that being income must be 3x the ask for rent. At least this was the case in Austin proper (i.e. inside the city limits, and inside the I-35, Mopac, 183 and Hwy 71 box), I saw similar requirements when helping a friend scout for a place in SFO.
When I was looking for a place I found a landlord willing to negotiate and haggle on the deposit since my income wasn't 3x the rent ask. They took a larger deposit, I signed a lease, wasn't late once.
As with everything, YMMV.
Yeah, that's the same question every scumbag landlord in America started asking themselves a few years ago when demand for rental units started going up.
You don't "need" to spend less than 30% of takehome on rent. If you assume you're going to be running in a treadmill your whole life, and you're satisfied working for subsistence only, then sure, go for it, blow half (or more) of your paycheck on rent. Lots of people in San Francisco and other expensive cities do this.
If you have life goals that don't involve being stapled to a desk forever, it's probably not such a good idea.
There are people out there paying 50% or more of their take home on their rent/mortgage I imagine - it's just not really considered to be wise move in most cases. 1200/mo for a 1 bed doesn't even sound that bad for what's supposed to be the most expensive city to live in America. I know people in DC who spend 1800/mo on a studio and that's pretty average. You could easily share a room and cut your rent in half if you were smart/willing.