As a cost/time enjoyment, videogames (particularly elden ring) are better than almost any other media.

If we're looking at a fresh AAA title, single player linear narrative (God of War) you're looking at £2 an hour.

Open world RPGs, Inc Elden Ring might be less than £1 an hour.

Multiplayer games (CoD etc) may have even better value, if you enjoy putting hours in.

Now consider what you want. To fund the huge cost of making a game in its entirety, you'd need a lot of money. Then the dev, publisher etc need a profit. So the ads have to be really really good value for the advertiser.

That means they have to be intrusive. Interrupting your narrative. Imagine in Elden Ring fighting for hours up to a boss room, you step into the fog and ...

BLAM... Do you need a razer thingymaboob? This thingy maboob is 1% better in three benchmarks that we chose because we liked that the numbers were higher. But it now only £1534 at your local store!

Every fucking time you die. 30 seconds of unskippable, poorly targeted dross. Screaming at you, begging you to buy their shit, and not their competitors.

It. Would. Break. The. Game.

It's actually much more common for both kidneys to fail together.

The underlying causes of kidney failure tend to be systemic (that is affecting the whole body) rather than local.

The big one is diabetes, and barring a blockage in blood supply to one kidney, the main damage is in all the tiny blood vessels that feed each nephron. This usually happens equally between both sides (although occasionally the renal artery stenosis is more of a problem, in which case one side can get a stent to try to maintain its function).

Other big causes are inflammatory/autoimmune. This means anywhere there's a kidney cell/structure the damage occurs. Broadly, this affects both sides at the same time.

The short answer is that you are correct. Routine tests, including the rate of urine production, the ability of the body to clear waste products (creatinine, eGFR, urea) may all be normal in the case of only a single kidney working.

It's not very rare to find someone with one kid ey by accident when doing a scan. These are caused by congenital issues that led to a solitary kidney or an issue in early childhood that damaged one kidney and not the other.

Occasionally there will be mild derangement of some of those values that lead to the suspicion that a single kidney is not working and the other is working much better.

In this case there are some tests that can be used. As one of the main reasons for kidneys to fail is blockages in the arteries that feed blood into them, an arteriogram can show if one kidney is getting blood while the other isn't. This can be done with an intravascular catheter, but is more commonly done with CT and arterial phase contrast. If one kidney is getting lots of blood, and something is blocking the artery to the other (renal artery stenosis) then it's a fair bet that the one not getting blood isn't working well.

Equally, structural differences can show if there is a blockage in the outflow of one kidney and not the other (unilateral hydronephrosis, where the kidney retains urine due to the pressure needed to push it through a narrow ureter).

Finally, the test that really shows this is a differential renal function test. This can be done in a variety of ways. One includes injecting a dye and seeing how much comes out of each kidney by CT scanning and looking at how much dye is in each kidney. Another involves the differential clearance of a radioactive marker.

As to why we have two of some organs and one of others: it's just evolution in action. These body shapes and functions arose and persisted because animals with these survived and thrived when others didn't.