Step-by-step explanation:
Imagine that, every day, by taking a look at your action plan you can clearly differentiate those tasks that you have to undertake before any other. Those that take you directly to your goal and you don't want to put aside because, otherwise, you would be delaying what you have set as your final goal.
Now imagine that, at the end of the day, by reviewing your action plan, you realize that you have achieved just what most focused on your main objective. In that case, your planning is working correctly.
Well, the priorities, in a simplified way take care of this, to take away everything that can hinder your course to your final destination and clearly indicate the way forward to dock at the desired place.