Earlier quoted context omitted.
You buy shares in the stock market, not dollars, so a crash shouldn't hamper your ability to retire, unless you want to retire during the crash itself (although diversity of assets would help with this). The stock market recovered years ago from the Great Depression and is doing really well again.
If you want to correct someone, please correct them properly. You buy shares or instruments traded on Exchanges, which make up the "Stock Market". However, you don't always buy on Exchanges (OTC/Over the Counter Trading). Those instruments can be equities (shares of a company) aka stocks, securities, futures, options, etc. The Dow Jones Industrial Average (a common benchmark index such as the Standard and Poor's 500)…
Shares are instruments [1]. (You say this later, but nobody buys "shares in instruments").
Exchanges, together with ECNs, OTC markets, broker-dealers, other market makers, buyers, sellers, arbitrageurs, investment banks, et cetera make up the stock market.