Just as deadlines are necessary, they are also arbitrary and unnatural at their core. They simply act as a forcing function to get things done.
To go to the moon “in this decade” was a deadline issued by President John F. Kennedy. It mobilized the funding and the will of a nation towards a goal. Necessary: yes. Natural: no.
Proving that two spacecraft can dock in orbit was a logical milestone achieved in the process of going to the moon (barely, as the mission was aborted shortly after docking was finished).
I often find myself explaining teams the difference between deadlines and milestones.
A deadline is like a high-speed locomotive coming towards you. Other than waking up in the morning, there is nothing for you to do. You will find the deadline closer to you.
A milestone, on the other hand, is a natural point of growth towards something. They require effort, planning, cunning, re-planning, creativity, and time. When my son started walking when he was 12 months old, he reached a milestone in his development. (It would have helped little if I set a deadline for him to start walking at 6 months.)
|A date.||A natural point of growth.|
|Manufactured and unnatural.||Logical and organic.|
|Often politically driven and aggressive.||Often technically driven and risk adverse.|
|Play it safe means to ask for an artificially early date.||Play it safe means to offer an artificially late commitment.|
Left unattended, milestones dominate the first half of the project schedule; deadlines the second half. Do not let that happen. Personally, I find that the trick to any successful execution is to continually align deadlines and milestones. Yes, this could mean delivering some degree of bad news at every alignment. But, just like eating some fresh fruits and vegetables with every meal, it may be good for everybody in the long run.