It has been repeatedly proven by studies that happiness is directly related to stress. The less stress you have in your life, the happier you will be. One of the best ways to reduce stress is by planing ahead. Your mind, your ability to think ahead and decide is your most powerful tool to reduce stress and determine the course of your life.
You might have heard the old question; "How do you eat an elephant?" to which the answer is "One bite at a time!". Challenges become manageable if you make a plan how to tackle them and set goals that are achievable.
In the end everything we do, is just everything we've done. So we may as well do it right, put a decent amount of planning and care into it and reduce the stress where we can.