A milestone is set taking into account all the possible factors that would come into play while completing the particular task. Missing a milestone would have a bad impact on the project since it would affect other tasks that are linked to the it. It would also mean putting a lot of things at stake while increasing the cost of the project. On the other hand, if the missed milestone was due to a major reason that would have affected the product in the near future and the deadline was missed due to failure of an important task then it can considered to be a link to future success to the project.