All software is a force multiplier, but some tools, like Zapier/IFTTT are in a class of their own.
Likewise concepts like Compound Interest and arguably knowledge of fallacies, such as "sunk cost fallacy".
What are some force multipliers that are available to most people, but which most people don't regularly put into use?
People get all worried about losing their followers & social connections. The social fabric is very adaptable. It does not require public technological codification. You realistically only need fewer than five good friends to be happy; text them. I can guarantee your followers don't care about you at all. The ones who do will reach out to you in other ways.
Since the OP also listed a fallacy, one in the same vein is the endowment effect - where people value things more simply because they already possess them. Consider the example of you holding a stock priced at $200. Now consider an alternate universe where you didn't own that stock but had $200 cash (plus some extra for transaction costs). Would you buy the stock? If not, you should probably consider selling it. This same thought process can be applied to nearly anything in your life: job, significant other, city in which you live. It's good for keeping you out of traps.