You can't invest in the s&p like that.

> Between January 1, 1963 and December 31, 2014, 1,186 index components were replaced by other components.

You can know an index of 500 large companies will go up but not know what companies will be on that index in the future.

You can sell when a component leaves an index and buy when a component joins the index and–guess what–that portfolio also goes up.

https://contrarianoutlook.com/wp-content/uploads/2018/02/SPY...

But you can invest in the S&P like that (through index funds), because the S&P tracks the performance of a rolling selection of stocks, not the backdated performance of a future selection of stocks that is unknown in the present.

Exactly, this is a fundamental fallacy of index investing—you can’t “buy the market” and any ETF that claims otherwise is a cleverly crafted leaky abstraction. The problem with leaky abstractions is that you usually have no idea that they leak until everything collapses...

BTC is different because it isn't backed by something like ownership in a company.

Also, there are different risks than equities. Equities have the risk of the company failing or being significantly impacted by many different things happening, while there are existential risks with BTC I feel these are often ignored or accepted as not applicable to most BTC investors.