A tariff-induced tumble for the Dow, S&P 500, and Nasdaq Composite paves the way for opportunistic investors to buy shares of phenomenal businesses at a discount.For well over a century, the stock market has been a bona fide wealth-creating machine. But this doesn't mean equities aren't susceptible to big moves lower from time to time.Between Feb. 19 and April 4, the mature stock-driven Dow Jones Industrial Average (^DJI -0.84%), benchmark S&P 500 (^GSPC -1.57%), growth-dependent Nasdaq Composite (^IXIC -2. ...