How the Stock Market Works Now: Elon Musk Tweets, Millions Buy

Welcome to the outsiders’ market.

It used to be Wall Street insiders—analysts, economists, investment strategists and portfolio managers—who fueled bull markets by enticing the masses to hand over their money.

Now, it’s outsiders—entrepreneurs like Elon Musk and Mark Cuban, rappers and rock stars like Ja Rule and Snoop Dogg and Gene Simmons of Kiss—who are firing up thousands, perhaps millions, of traders and investors. They have blown away the old myth that Wall Street is the exclusive keeper of the keys to wealth, which it will share only with those who are willing to pay a fee.

Unfortunately, a new myth is in the making: that the outsiders know for real what the insiders only pretended to know.

If your timing was right, you might have made a lot of money over the past few weeks by following Mr. Musk into bitcoin, Mr. Cuban into dogecoin (another digital currency), or the venture capitalist Chamath Palihapitiya, who has more than 1.3 million Twitter followers, into GameStop Corp. stock or options.