A common problem I have seen when companies try to switch to scrum, is that there are no clear goals for the team. The team members are experts on converting a story to functionality but they need to know what the goal is, where they are going. It is hard (or impossible?) for a team to get anywhere if they don’t have a clear and common goal. The goal is set by the product owner and the tools are the stories and the backlog.
It is very important that the product owner makes good use of the sprint planing meeting by setting goals, motivating and engaging. Bad sprint planning ==> very likely that the sprint fails. A good team may help the situation, but the product owner is important. If You are a product owner and usually arrives at the sprint planning meeting with a bunch of poorly prepared stories from a chaotic backlog, You should probably sit down and reflect over what this behavior leads to in the team.