The One Line
Boiling down your reasons for a particular action to one sentence may sound simplistic but it is a very helpful exercise.
Doing so forces you to distinguish between the essential and the marginal. It also causes you to select the point of greatest priority among the essentials. Without such self-constraints, you can easily pour in so many points that your perspective becomes obscure.
As you know, major corporations condense their products to one word. [Disneyland sells Fun. Southwest Airlines sells Freedom. Revlon sells Hope.] Compared to the one word approach, crafting one line is easy.
One clear line makes it easier to communicate your key point to others. The single point presents a much smaller target to potential critics than a multitude of reasons.
Why should you be promoted? Have your supporting analysis but give the reason in one line.
Why should a disciplinary action be taken? Tie together the evidence with one connecting line.
Why should you buy a particular car? Once again, one line.
It's no guarantee that your decision is best but it can help you along the way.