Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
Maybe, like us, you have had the experience of trying to straighten up a closet and getting distracted. While you are organizing a shelf, you discover that box of networking cables you had been meaning to sort through. Then you come across that broken webcam and you remember you now have the missing part, and start to fix it, but you cannot find the cable. Then you discover another box with cables that need to be sorted and cleaned out. . . Before long, you are 2 hours into a task on which you had planned to spend only 10 minutes.
Development can be like this. Even really great developers can get distracted with tangential work. What started out as a 1-day project can quickly explode into a weeklong project if not planned and managed well.