It is said that those who do not learn from the past are doomed to repeat it. That implies that avoiding the mistakes of the past means preparing in the now to meet the future. Those who take the "eat, drink, and be merry for tomorrow we die" approach to life will be swallowed up by cunning and well prepared enemies (temporal and spiritual) laying in wait to snare those who fail to prepare, such will deserve exactly what they get.
No man is an island so always being happy in the now is dependent upon preparing, in a world full of people living in the now, for tomorrow to become the now, which it always does and those who ignore its coming are often disappointed by its arrival. I too hope for happiness and peace for all but I am not foolish enough to sit idely by with nothing but hope to go on, I will do everything in my power to stack the deck (so to speak) so that happiness and peace has the best chance I can give it to become a reality. For me that includes listening to others whom I consider to be wiser than myself. The wisest of us all is God and His only begotten son Jesus Christ. Doing so always prepares one to meet tomorrow regardless of how easy or difficult it may seem.
Understanding "Who I am", "Where I came from", "Why I am here", and "Where I am going" is extreamly important and most certainly demands that I consider the full spectrum of possibilities and then choose wisely the path I will take. To do that requires that I learn from the past (others as well as my own), paying attention to the present, and preparing for the future, all the while looking to divine guidance to make sure I get it right. We only get one shot so getting it wrong is not an option any of us can afford to risk.