Requirements Engineering: Understand why who is doing what for whom

If youIf you
...want to have something
...want to buy something
...want to make something
...want to do something
...want to do something for someone
...want someone to do something for you
...want to do something with someone

then you have requirements.

then you need to understand each others requirements
HOOD helps you to define requirementsHOOD helps you to understand requirements