So, concretizing your claim, we get:

• A majority of the people who know enough about investing to know that they should invest in index funds rather than something else, do not do so, instead continuing to invest in other, less-optimal financial instruments.

I find this hard to believe. Do you really have anecdotes supporting this? (And a lack of a comparable or greater quantity of anecdotes to the contrary?)

• A majority of the people who possess enough knowledge about nootropic drugs to be able to figure out that they should take modafinil, do not take modafinil.

I am entirely unconvinced that taking modafinil is a good idea, so you would have to first demonstrate that.

• Something about Bitcoin. I don't know what your claim even means in this case, honestly. Please explain.

I think your post would greatly benefit from the inclusion of some of those anecdotes you allude to. In other words, why do you believe this thing you believe? What has caused you to come to this conclusion? I would love to know!