Things inevitably go wrong in the training process. You develop injuries, you experience flat weeks, you have bad races, and so forth. Figuring out the cause of each setback will help you reduce the number of future setbacks you experience. Your training diary holds much of the information you need to successfully troubleshoot your setbacks. For example, in looking over your training diary during a period of injury, you might discover that you tend to get injured any time you increase your weekly running mileage above a certain rate. Armed with this information, you can hold yourself below this rate in the future and minimize your injuries.