There's an idea so pervasive that it almost doesn't get questioned in media: that media agencies – the people who place ads on behalf of most big advertisers – are largely staffed by 25-year-olds who only consume social media. There is some truth to that – but it's more complicated than it appears. Alex Radford and Richard Thompson run an independent media agency named D3, and join Duncan Greive to break down how media buying works, and the ways the search and social giants' products eat budgets – including a revealing view into the black box that is the Google ad tech stack. Learn more about your ad choices. Visit megaphone.fm/adchoices