60 Minutes said most stock trades are made by computers without human involvement designed by math wizards for pennies of profits per trade over billions of trades. Milliseconds become important to beating the competition (other computers) by being faster. Getting close to or in the stock exchange buildings has physical effects.
Of course, a bad algorithm or synergy of algorithms can crash the stock market. Getting to the point where no one really understands the system is pretty risky which is why people trade stocks, right?