Most (all?) people have to do hishtadlus for parnassah for whatever reason. How do we know what's hishtadlus? Who said opening a business is hishtadlus as opposed to spinning and doing jumping jacks?
That's sort of what I'm asking.
Okay, that's an entirely different question. (That was Motzei Shabbos Vaeira. I'm only half kidding.) The short answer is that there are two schools of thought.
One requires a basic level of hishtadlus because the lack of it commonly causes a lack of fundamental needs fulfilled: that is, it is normal for those who do not put in this hishtadlus to lack their basic needs. As such, this hishtadlus is incumbent on everyone.
The other school of thought says there is a measuring stick, the manifestation of emunah - bitachon - which precludes hishtadlus. This is entirely dependent on the person. If you lack bitachon (and thefore, menuchas hanefesh) regarding a certain outcome, hishtadlus against that outcome is required. If you aren't worried about it (not out of a lack of responsibility / head in the clouds but out of bitachon, the nuance of which is beyond many and a Rebbe is needed), no hishtadlus.