That reminds me of Robert Sapolsky's theory that we have no free will, none.

Watching that (he looks like a lone survivor on a deserted island), i kinda see why The Church in the 500's banned philosophy, then why it got new-normal re-banned at universities (in favour of THE Science).
At first sight, philosophy can be scary. Even to normal people programmed not to question things, but especially to the GODS, who are running the progamming. It runs the risk of fucking up their whole premise for control.

The idea that we don't have freewill is as scary as it gets.

Satre, as i recall, was the opposite side - there is freewill - it's the defining human quality - you can always choose.
Mulling it over after you posted, my observations/views align more with Sapolsky's observations/views.

My theory is that people are just like water -- we follow the easiest path, period. Water never flows up, even in Taitung! "But what of the person who runs into a burning house to save a stranger?" My response would be that for that person, for whatever reason, doing that is easier for them than doing nothing; in other words, it would be more painful for them to do nothing than to risk injury.

Great theory. Simple - but profound. Also got me thinking ... have long had this thing with Efficiency as a key driver. We're always aiming for the most efficient way to do something - you learn how to do something, then you learn how to do it faster/more efficiently.
Which is similar to the water flows downhill analogy - we're programmed to find/refine the path of least resistance.

There are instances of bad choices though. I've made em. Not in my best interests. I know that coz i regretted them.

With the person running into the fire, let's say it was too late, the stranger died, the person who ran in suffered 3rd degree burns, lost their lucrative job as a model ... then they got addicted to pain medication drugs, behaved erratically, whereupon their partner left them & they lost custody of their children ... & finally their home in the divorce settlement.

I agree that actor was motivated by your water-flow theory in his decision for the reasons you outlined.
But, it can still be a wrong-headed decision producing the opposite outcome of what was intended.

Which is where Sapolsky's view gets interesting - there is all this massive accumulated stuff from the past that goes into influencing every decision in the now. He identifies childhood trauma as an obvious de-railing influence-factor on a person's decision-actions, but expounds that beyond our own lives - there's also this whole cultural history bearing down on every decision-action.
Doesn't leave a whole lot of room for free-will!

Which raises the question of whether there is an adjustment zone in a world without freewill?
A zone where you tend to make more good non-freewill water-flow decisions than bad ones? Where you sail through, as some people seem to do.

My limited gleaning from Sapolsky suggests this may be the default setting, but it's impacted by ... impactful events - which, by definition, are out of your control.

The other thing is, the path of least resistance implies that there is a force of Resistance - what's that exactly?