It's true! Imagine a team of experienced, competent agilists. Now give them a poorly written, shoddy, unkept backlog. Will they prosper and thrive? Not without upgrading that backlog. On the other hand, if you take a team that is underperforming and provide them with a clear, thought out and well-written backlog you can bet they will start improving. The fact is that your backlog is a major component in your agile success and as a group, we don't pay enough attention to our backlogs.