Milestones are intermediate targets designed to keep you on track toward your main deadline. They help you make continual progress over time, so you don’t have to accomplish everything at the last moment.
For example, suppose in November you decide to lose thirty pounds by the time you leave for vacation the following July. To help you meet your deadline, you might set a milestone of losing a pound every week. If you meet each weekly milestone, they by July you will have lost all thirty pounds. If you miss a milestone or two, you still have time to take corrective action - before it’s too late.