The theory that rich people will spend their money on either useless crap, or hire people for their personal or corporate businesses - either way, other people further down the food-chain will get paid. Because as we all know, poor people can't pay other poor people. You want a job that pays actual money? The Trickle Down Theory means that the rich guy will be the one to sign the check. The Trickle Down Theory works for other non-rich folk too. They get paid, they go to the store to buy stuff - which means the money goes towards helping the economy, and helps pay the salary of other poor folk. Ok so the rich idiot diva daughters get $200,000 cars, but the guys that build and paint and ship and sell those cars get paid for it. They in turn can pay others who do other jobs and spend money at other stores and services. See how that works? That's the Trickle Down Theory.
Poor Guy: "This blows! I need a job so I can pay my rent."
Other Poor Guy: "Sorry dude, I can't afford to hire you since I'm poor too."
Some Rich Guy: "Hey, I'll give you a job and pay you some of my rich-guy money to do it! You make money, I get a job done, it's win-win!"
Poor Guy: "Yay! The Trickle Down Theory