This is definitely something that I could agree with when it comes to the classroom and how a teacher needs to be prepared. Things can and will go wrong and as a teacher I find it challenging as well as exciting to have to adapt and change at a moments notice. "Chance favors the prepared." This is a quote that I have always tried to follow. Essentially the teacher who prepares for alternative plans is the teacher who is one step closer to becoming a great teacher. I constantly find that things happen even to the best laid plans and if I haven't prepared or thought of an alternative for just such a case, then I will be at the mercy of the students.
Boss, S., & Krauss, J. (2007). Reinventing project-based learning. Washington, D.C.: International Society for Technology in Education.