Long before credit cards and even electricity, society was learning how to extend credit. The concept is very simple. If someone wants to borrow money or pay you later for goods or services being delivered today, then the lender needs to determine the likelihood that the borrower will live up to their promise to repay.
The same is true with buyers and sellers of equity (stock). The buyer (investor) needs to determine the likelihood that the seller is giving an honest assessment of the opportunity. The buyer needs to assess the merits of the opportunity and most of those are tied to the people running the business. Today there are many tools and third party opinions that influence a corporate finance (investment) decision, but the CORE decision still is whether the buyer trusts the seller. That will never change.