It's almost entirely about paying less in fund fees and aiming to be 'average'. I.E. get the return of the market rather than trying to beat it. Think of it as 'passive' investing rather than index investing.

EDIT: But yes, we don't know whether one can assume "The S&P500 will average 10% per year for EVARRRRR!!!1".

I'm not the OP or the grandparent post, but I wonder what happens if a significant portion of the market starts indexing? My gut is that there are strong incentives against that: as more people start indexing, the gains from not indexing become more diverse.

On the same token, more indexing will insulate losses by creating an implicit demand based on market cap.

You realize that the scenario you describe is equivalent to "the entire collapse of global civilization that will make previous dark ages look like candy and unicorns."

I'm serious. If the overall economy is "stagnating or even deflationary" for any significant period of time, all of the wheels are going to come off.

(Really want a dark thought? You realize that we've dug up and used all of the easily-available oil, right? When Some Later Generation Gets Its Act Together, they aren't going to have a convenient, cheap source of energy.)

Yes, parent poster said that index funds "seen as this wonderful thing that cannot go wrong." But nobody who knows anything about investing sees them that way. Index funds invest in stocks and bonds, a broad index fund will pretty much mirror the market. But the market, even the market as a whole, is far from safe.

What an index fund does guarantee is that holders of the fund will do better than the average of the "active" investors, who try to pick and choose the best stocks in the index (which for a broad index is basically "the market"). This is because the active investors, as a whole, receive the "market return", but they do so only after investing resources in researching the companies (which index funds don't do) and because the active investors trade a lot, relative to the index fund, so the active investors incur much greater transaction costs. An index gets the market return, but without incurring the costs active investors do, so the index is certain to have a better net return than the average of all active investors. This doesn't mean that index funds are "a wonderful thing that can never go wrong". It's certainly possible for the market to tank, in which case it's little solace for index fund holders that they beat the performance of the average active investor.

> (Really want a dark thought? You realize that we've dug up and used all of the easily-available oil, right? When Some Later Generation Gets Its Act Together, they aren't going to have a convenient, cheap source of energy.)

Plenty of nuclear fuel still around, on earth (uranium, thorium, hydrogen) and in the sun (solar power, wind, etc).

Information can no longer die - CDs, DVDs, libraries - a new dark age will be mercifully short.

And as for cheap energy - there are plenty more, better sources than oil.

Digitized data is replacing physical storage, and that makes it ephemeral.

How would you read a DVD without a player? Can you rebuild the player, without specs? Can you rebuild the filesystem, or the decoding?

There is plenty of cheap energy that isn't oil--unfortunately, the exploitation of it without oil reserves to bootstrap with may prove impossible. That's the point being made here.

With a microscope and a few pages of spec I think you can read text off a DVD.

But yes that's not a disaster-friendly method.

That's not how it works:

https://en.wikipedia.org/wiki/DVD

Perhaps Dylan might an electron-microscope?

The pits are about a micrometer in length. That doesn't take an electron microscope.

> Information can no longer die - CDs, DVDs, libraries - a new dark age will be mercifully short.

Well, also, the printing press was invented a long time ago, so we actually have loads and loads of dead-tree copies of the really important stuff.

I would argue that while information can't die, expertise and built up production capacity certainly can, and I think that's even more important. I could read all the books I wanted about how to build a plane, but I highly doubt that I'd have the first clue where to start.

Cheap energy, yes, but...

Scenario: you're living in a medieval village. Project: build a thorium reactor. Step one: ???

Medieval villages didn't use oil either. Have to get past that point. Have some oil-seed crop, sufficient population, trade with large cities. Then - buy antique samples of thorium and uranium, put in a pot - they melt and give off heat. Not too complicated really.

Like @kspaans says it's more about buying a representation of the market i.e. passive investing. Though, in the case of the S&P500, 500 large cap US stocks is hardly buying the market, so a keen investor would try to create a truly diversified portfolio including domestic, international, equities, bonds, real estate, commodities, etc.