The chief and fundamental incentive in a human being, as in an animal, is egoism, i.e. the urge to existence and well-being.
This egoism, both in an animal and in a human being, is linked in the most precise way with his innermost core and essence, and indeed is properly identical with it. So all his actions, as a rule, spring from egoism and the explanation of any given action is always to be sought in it ﬁrst of all; and likewise the calculation of all means by which one attempts to steer a human being towards any goal is also entirely grounded upon it. Egoism is, by its nature, boundless; the human being unconditionally wills to preserve his existence, wills it unconditionally free from pains, including also from all lack and privation, wills every pleasure of which he is capable, and even seeks where possible to develop new capacities for pleasure. Everything that opposes the striving of his egoism arouses his unwillingness, anger, hatred: he will seek to destroy it as his enemy. He wills where possible to take pleasure in everything, to have everything; but, since this is impossible, at least to master everything: ‘All for me and nothing for the others’ is his favourite saying. Egoism is colossal: it towers above the world. For if the choice were given to any individual between his own destruction and that of the world, I do not need to say where it would land in the great majority. In line with this, each one makes himself the mid-point of the world, relates everything to himself, and with everything that happens at all, e.g. the greatest alterations in the destiny of peoples, he will relate it ﬁrst to his interest, however small and indirect it may be, and think about that ahead of everything. There is no greater contrast than that between the high and exclusive concern that each one has for his own self and the indifference with which all others as a rule regard this very self; as he does theirs. It even has its comical side, seeing the countless individuals each of whom, at least in a practical respect, takes himself alone as real and regards the others in some measure as mere phantoms. This ultimately rests on the fact that each is given to himself immediately, while the others are given only mediately, by way of the representation of them in his head: and immediacy asserts its right. For in consequence of the subjectivity essential to each consciousness, each is for himself the whole world: that is, everything objective exists only mediately, as mere representation of the subject, so that everything constantly depends upon self-consciousness. Each carries in himself, as his representation, the single world that he is really acquainted with and that he knows about, and he is therefore its centre. For this reason each is all in all to himself: he ﬁnds himself as the owner of all reality and nothing can be more important to him than himself. But whereas in its subjective aspect his self presents itself with this colossal magnitude, in the objective aspect it shrinks down to almost nothing, namely around one seven billionth of humanity now living. Meanwhile he knows with complete certainty that this very self that is important above all else, this microcosm, of which the macrocosm, or his whole world, appears as the mere modiﬁcation or accident, must be extinguished in death, which for him is thus synonymous with the extinction of the world. These, then, are the elements from which egoism grows on the basis of the will to life, and constantly lies like a wide trench between one human being and another. If someone really leaps over it to help another, then it is like a miracle that provokes astonishment and wins applause.
From the Essay on Morality