To Exist For A Better Cause.
I used to think that humans exist for their own sake, and to seek happiness is the sole purpose of life. I am the center of the world I live in, and my self-consciousness constitutes the world. Therefore, how I perceive my surroundings, how I care for my feelings, and how I think about my situations are the only questions that I have to consider.
This thought is dangerous, to myself and to humanity. The anthropologic centering of human individual and human species blocks any further development.
Looking back at the history of western philosophy, human beings are indeed the main subject that philosophy concerns with. But not a single branch of philosophy posits humans as the sole being in the world; it does not limit itself within the boundary of human beingness but opens itself to other possibilities that are not grasped by human beings (such as Plato's forms, Aristotle's immaterial substances, a lot of philosophers' Gods, Kant's transcendence, Nietzsche's Übermensch, Sartre's Other, Lacan's Real, Heidegger's Dasein...) For human nature is characterized by finitude, and the nature of this finitude is its recognition of itself (or the infinite would not exist and thus finitude has no meaning). This authenticity and openness are the powers of finitude. Humans' attempts to seek the ultimate being do not terminate with each failure. On the contrary, the failures strengthen our curiosity and motivate us to move towards our invisible limit.
At the very beginning of the history of philosophy, Aristotle proposes the existence of truth by characterizing humans as the only living things that are capable of reasoning. His model of the three souls (vegetative, animal, and human) puts humans as the "highest" being on the ladder of the living things. With this rational faculty, humans can combine different sense information and abstract concepts. Beliefs and judgements are thus formed to establish a correspondence between reality and opinions. It is only then truth and error can be spoken about. It is obvious that Aristotle does not doubt the existence of an objective world outside of human consciousness. Universal truth is a given reality for human beings.
Later in Existentialism, Beauvoir's idea of ambigiuty, Sartre's idea of being-in-itself and for-itself, more clearly characterize humans as an ongoing lack, with desires and needs ever evolving. Without an external elements, it is impossible to form a self, for it is always changing, and changes can only be stimulated from interactions with the outside world.
The thought of life's purpose for happiness blocks any possible objective reflection, a third person narrative, and a relation that one creates to live with oneself. Misappropriation of happiness could lead one towards self-destruction - or maybe that's too serious of a consequence, and that's the ending to human life anyways.