The adverb “ευ” as a prefix is inherent as a synthetic in many words. Specifically, eu means "good", as we find it in the words like eulogy, euphemism, euphoria and euthanasia.
The word demon has a long history and today it is used as an oxymoron in relation to its meaning in antiquity which contained semantic piety. In Homer "demons" were originally called the gods, while in Hesiod "guardians of mortals". Thus, the first meaning is "god, goddess". It follows the meaning "fate, destiny, adherent, luck". Therefore, a demon is one who "shares", gives fate to every human being or otherwise who defines it. As is well known, the gods were numerous, but also anthropomorphic. Despite their coexistence, however, the demon declared, above all, an impersonal and indefinable impersonal force, an intangible form. Plato distinguished them from the "visible gods" according to the previous poets, as children of gods in Timaeus. Diotima in Plato's Symposium, speaking of Love, refers to the "genus of demons" as the "intermediate between the mortal and the immortal", that is, in the middle between the two and fills the gap, so that the universe is an indivisible whole ". Through the mediation of demons, the communication between gods and men takes place. Plutarch refers to Socrates the Demon as a kind of higher life guide. Plato, in Socrates' Apology, identifies the demon with a voice within him, "preventing him from doing something, but never urging him". The demon contributes to his faster completion or deification, as long as the mortal perceives the "percussions" and "hears his voice". The demon is commanded to bring back to heaven the fallen man on earth. Plato the Demon is characterized by the immortal-divine part of the soul located in the upper part of the human body and aims through wisdom and truth to lead to blissful life and immortality.
In summary, Eudemonia means that a man has plenty of demons (spirits) that bring him closer to the divine, and while happiness can be a part of this, most remarkable works of our lives will not always bring us joy and satisfaction, but they are well worth pursuing. Actually, Aristotle does not say we should seek eudemonia, but takes it for granted that we already do.