Full Idea
We do not wish for impossible things - for immortality, for instance.
Gist of Idea
We all assume immortality is impossible
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1111b22)
A Reaction
Obviously this primarily means physical immortality, in contrast to the immortal gods, though Aristotle doesn't seem to believe that humans have an immortal part.
Book Reference
Aristotle: 'Nicomachean Ethics', ed/tr. Irwin,Terence (rev Reeve) [Hackett 1985], p.39