A similar but not quite the same mechanic is fuel economy.

Let's say you have two vehicles, both doing 10,000 miles per year. One gets 10 mpg and the other 50.

Would you rather upgrade the 10 mpg vehicle to 13 mpg, or the 50 mpg to 100 mpg?

Not only should you pick the former - you should pick the former even if you could upgrade the 50 mpg vehicle to run on nothing.

Yes, the fuel savings in the former case are larger than the initial fuel consumption in the latter case, but is it really unintuitive in practice? What I mean is that we generally pay for fuel per volume, not per mileage. Now, I am not sure about others, but I would always base my decision based on the money I'd save over a period of time, which in this case would require considering each vehicle's actual fuel consumption over that period of time.

It is the assumption that the two cars always make the same number od miles indepedently od the cost that is unusual and unintuitive.

If you think of it as a family that keeps obstinately driving both cars the same amount despite massive cost differences its weird but you could think of it as a mixed fleet of delivery or work trucks that are all needed regardless, the question is how you manage or prioritize upgrading them.

A similar example with league of legends:

One point of resistance gives 1% effective extra health no matter how much you already have.

100 armor give 50% reduction (100/100+100) while 200 armor give 66% (100/100+200)

The percentage 50 -> 66% is shown ingame and players often think the value per point of armor drops.

What does actually happen is your effective bonus health changes from +100% to +200% and every additional point will be worth the same

Interestingly, the same logic applies to vaccination rates. Going from 0% to 5% vaccination has no impact on the course of the pandemic (except for those few vaccinated people, of course). Going from 75% to 80% has a much larger impact, and could stop the pandemic in its track (depending on R_0, and many other real-world complications of course).

(And the reason is just the same: what matters is the remainder.)

OK, let's assume you have 75% elemental resistance. You also take 15% reduced damage and 10% less damage. You have 5% chance to avoid elemental damage and 10% to dodge it and are under the effect of Elemental Equilibrium and Gluttony of Elements. How much better is it to just kill everything before it can kill you?

You joke, but PoE's use of stuff like 'increased/decreased' and 'more/less' to distinguish between additive and multiplicative calculations is one of the smartest game design decisions I've seen.

The game has a lot of seemingly arbitrary distinctions and concepts that you just have to learn over time, but once you actually learn them, the consistency of it all makes it very easy to handle the large amounts of complexity in the game.

It's completely unbearable going back to other games that just say crap like "+30% to x" without actually distinguishing between the different ways calculations can be done, forcing you to either experiment endlessly, look up every tiny thing on a community wiki, or just wing it.

It's a nice contrast to something like WoW where every time you get a new item you just chuck the item code into some ten million LOC simulator and fuck around with limiting permutations until it doesn't take 15 minutes to run, just to find out through some totally opaque process that you have 189 more dps. And then 2 months later you find out there was a bug in the simulation and the item you deleted 1.9 months ago was actually better.