tl;dr:A comment is usually a sign that a piece of code needs refactoring. Greg wants us to ask "could I refactor the code to remove this comment?" The answer is typically yes. He highlights three common examples of comments.
tl;dr:Businesses are date driven so should engineering teams be. It's a hard skill, and when estimates are wildly off, there's an opportunity to introspect and improve. Meeting estimates build trust. The key is communicating feature changes and tradeoffs with the business early on.