Although proper use of project management tools can definitely mitigate the risk of pitfalls, as wms7 mentioned, even in relatively simple projects, the unexpected will almost always happen. However, when you use these tools effectively, they can be very useful in managing unexpected events that do occur. If you keep your Gantt chart updated, it is very simple to assess the impact of the unexpected event on all of the tasks in the project, and it can be adjusted to see how tasks can be moved around to have the least impact on the project. If you are not using project management tools properly, this process of reassessing and deciding upon a path forward can take much longer and will be very inefficient.