This is stated over and over by people who like big companies, like an axiom. And like an axiom, it's impossible to prove - because the only way to prove it would be to compare it against something that doesn't exist, a United States without trillion dollar companies. So you're supposed to just believe it because of how often it's repeated. But I don't believe it, on the contrary, it smells like bullshit to me. It reminds me a lot of another financial axiom we were all supposed to believe: trickle down economics. And look how that turned out.