Attention is a limited resource. There's just 24 hours per human per day, and every advertiser wants it. The attention economy has always existed—penny papers competed with each other the same way streaming services do now—but today we feel it so much more because our devices are no longer plugged into walls; we can take them with us, to have entertainment and knowledge wherever we go. But if only it were just those two things. Tristan Harris, a design thinker and former ethicist at Google, explains how advertising has become increasingly persuasive and tailored in the age of big data. Companies sell users' attention and personal information to the highest bidder, who uses it to manipulate thoughts and beliefs—be it about products or politics—with very little transparency. This critically undermines our free will and democracy. "So many of our institutions depend on us having sovereign minds and sovereign ideas," Harris says. It's time to start rigorously questioning advertising's business model, and reorganize the attention economy to align with public wellbeing. To find out more about Tristan Harris, head to tristanharris.com.