Over the last few years while working in numerous scrum teams, I have come to realize one thing that all of us seem to struggle with - completing user stories within sprint boundaries. The most common reason is the long list of tasks we have at hand. Tasks that need to be completed so that a user story can be accepted. Delay in any one of the tasks usually leads to the story spilling over to the next sprint. After a detailed introspection of the scrum, I often find that the only way to avoid delays is to diminish the unknown factors in a sprint and have a better plan. In other words carry out effective backlog grooming. Unknown factors can range from UX layout issues to crystalizing requirements for setting up a test bed.