Answer: Because planning allows you to draw a guide on how to do things.
Explanation: The planning is order and when there is order there will always be better results. If a person has a goal and it is planned, it is more likely that she will get what she wants since she has traced a path, she has created a way of how to do it.
Planning helps you know what to take into account and what not. It allows you to focus on the important details and put aside things that can only serve as a distraction.