Just thought I'd throw this out there because I often come through here looking for some interesting strategy stuff to weigh in on and my lord the amount of river hero fold spots is crazy. These spots are incredibly player specific and you will most likely never see them again, what's more, if you can't work out a way to make money here you can just hit fold and it costs you nothing, there's no equity you're getting pushed off or anything like that, you can just ditch your hand because you don't want to invest in something where you're unsure of the returns. I'm not saying that you can't get better at these spots but the way to hero fold river is not to gain an encyclopaedic knowledge of every river spot.
This brings me onto my next point, poker is (at least in my personal opinion) about the turn. Flops have a ton of mixing so unless you're playing against very very good players it's hard to go too wrong and rivers tend to play very easily when you have a good understanding of turn ranges. My thought process on rivers usually just comes down to: do they get here with enough reasonable looking bluffs? What about too many? Do they need to give up with a fair few of them that they might not? This process works really well because most regs are actually pretty good at firing the third barrel when they get there with a nice looking hand (i.e: not a missed fd) BUT most of the time they will not actually get to the river with a nice well constructed range that enables them to have adequate bluffs on every run out.
Here's an examples to make this clearer: you're in the BB after defending a BTN 2.5x open, you have Kx8d on Kd9d4x2xTd and you're facing a triple barrel sized as 1/3, 150%, 50%. This seems like a really close spot, we've got blockers and everything, but if you know that the person you're up against misses double barrel with hands like Ax with 1 diamond or just random undercards like 75 then what do you know, you have a super easy fold because they just don't have those hands to bluff here even though they are sizing pretty small and don't need to bluff that often.
So next time you're in a sick river spot that has you hating your life ask yourself how well you understand the turn here and go back to that and then hopefully the river will make sense of itself.