As Dr. Simon said in an earlier lecture, the end result or product of your project is never exactly the same as what you planned it to be. One of the reason for that is/could be because of milestones missed. Now, the change in the project can be a good thing or a set back depending on how well one can compensate for the missed milestone. For example, your team is working on building a table. midway through the project, you find out that you missed the deadline to buy the legs of the table from the only vendor that had them and now they are out of stock. So you compensate by buying another set of table legs and it can end up being much more functional and elegant (in which case the change is good) or you come to the finding that no other legs fit your table and you must start the design over again. So, missing a milestone can go both ways to help or harm a project. It depends for every single project. This is why in the PERT chart, we draw out other options or pathways to take if anything is missed and would cause harm to the project. It’s better to be prepared for such cases and just not hope that maybe something good will come out of the milestone being missed.