tl;dr: Carmack reflects on id Software mistakes: Quake was technically over-ambitious (Doom++ would've sufficed for multiplayer/modding before pursuing full 6DOF), he pushed the team too hard at unsustainable startup intensity, and the founders' stock buy/sell arrangement created bad incentives versus standard vesting. He also acknowledges that requiring level designers to have both gameplay and strong visual design skills was reasonable, but the company should have paired artists with designers sooner instead of letting infighting fester.