Without an appreciation for the gemba, where the data was collected, it is easy to be mislead by the data.
The most common waste of effort in examining data is reacting to the expected variation of a system as if it is something special. We have discussed this in many previous posts, for example, We Need to Understand Variation to Manage Effectively. After that, I think there is a good chance of failure to appreciate what the data is, and is not, telling us based on mistaken assumptions about what the operational definitions were...
continue reading: Data is Important and You Must Confirm What the Data Actually Says