Being a project managers is not easy, it is a position that requires a lot of experience, responsibility and good organization skills. My boss is a project manager with a very broad experience in Electrical Engineering projects. There was this time that we were doing a project for a very important person from the government. Our boss knew that doing the project in an excellent way would make the customer to come back for more. The project involved the installment of multiple electric motors. When the project manager did the schedule for the due dates, he added 3 extra days because he had his reasons. He told me that the type of electric motors we were ordering were very rare and that could possibly cause a delay. The delay happened exactly as the Project manager told me it would, but since he had added 3 more days for the due date we were able to finish the whole project on time. I believe that this kind of things can only come from experience. There is no way somebody could predict that some products will be delayed or not. Hope you get something out of this example.

Sincerely,
Roberto Pineda.