A very common mistake that Agile teams make is when they try to design the software in their planning sessions.

I can kind of understand the temptation. The developers don't really know what's going to be involved in implementing each story, and the project manager wants accurate-ish estimates. So they dig a little deeper. And the danger is that they'll dig too deep, and then keep digging, leading to a monumental design effort lasting hours - or even days.

It...