Why do people always assume that happiness is the ultimate goal in life? Is happiness even that optimal?

For example, people always say stuff like, "do what makes you happy" or "money can't buy you happiness." But then people talk about the hedon treadmill where you don't really get happier after achieving your goals. So, it's all just temporary.<br><br>Meanwhile, there is the concept of flow where you have the most enjoyment, happiness, pleasure, and fulfillment when you focus all your attention on something and you exercise your skills to meet the challenges. It improves your performance and you are completely absorbed in the activity. But the problem is that you can achieve this state of flow through many different activities, even negative ones that aren't good for you like crime, substance abuse or other addictions.<br><br>Lastly, ancient Greek philosophers like Aristotle thought that optimal living was living with virtue and that happiness was a byproduct of it. But they also thought that virtue was based on our nature as human beings with reason. The question is, what is the ultimate goal of our nature? Or do we just make up arbitrary goals for ourselves?