(and yes, I know, this has very little to do with sprints directly)
We don't blame, we solve.
Easily the biggest hindrance to a successful project is in-fighting and finger-pointing. This isn't a game, nor is it life-or-death. It's a project. We're very smart people trying to solve some very complex problems. Mistakes will be made. No one will die. Money, on the other hand, may be lost. Let's not let it get to that. Paychecks are nice.