Tim Roughgarden, speaking at the Institute for Advanced Study's Members' Colloquium, takes on a long-standing folklore belief in economics: that simple auctions perform well precisely when bidders treat the items for sale as substitutes rather than complements. He asks how this intuition, drawn from real mechanisms like 5G spectrum auctions, can be turned into a precise mathematical conjecture, and what tools might actually prove it. The core move is a transplant: lower bound techniques normally used to show limits on polynomial-time algorithms or on polynomial-communication protocols turn out to apply directly to the equilibria of auctions. Roughgarden walks through this connection between computational complexity and auction theory, showing how nondeterministic communication complexity becomes the right lens for a question that originated in market design. The talk runs just over an hour and assumes some comfort with both algorithmic thinking and basic auction theory, rewarding that background with a genuinely new way of looking at an old economic puzzle.