Sprint Planning Meetings: A Guide to Better, Smarter, More Efficient Iterations (7pace.com)

"Do a sanity check". Probably one of the most important things that is often overlooked.

Back when I worked in agencyland, capacity and time tracking were the most overlooked, underestimated factors in a project. The POs and PMs I know now would say the same. When a project goes off the rails, it can too often be traced back to one or both of those issues.