Bluematter.

Xenophon, Works on Socrates:

I once heard him discuss the subject of estate management (in Greek: οικονομία, economics) in the following manner.
“Tell me, Critobulus, is estate management the name of a branch of knowledge, like medicine, smithing and carpentry?” “I think so,” replied Critobulus.[...]

“But what do we mean now by an estate? [5] Is it the same thing as a house, or is all property that one possesses outside the house also part of the estate?”
“Well, I think that even if the property is situated in different cities, everything a man possesses is part of his estate.”
[6] “Do not some men possess enemies?”
“Of course; some in fact possess many.”
“Shall we include their enemies in their possessions?”
“It would be ridiculous, surely, if one actually received a salary for increasing the number of a man's enemies!”
[7] “Because, you know, we supposed a man's estate to be the same as his property.”
“To be sure--meaning thereby the good things that he possesses. No, of course I don't call any bad thing that he may possess property.”
“You seem to use the word property of whatever is profitable to its owner.”
“Certainly; but what is harmful I regard as loss rather than wealth.”[...]

[10] “That is to say, the same things are wealth and not wealth, according as one understands or does not understand how to use them. A flute, for example, is wealth to one who is competent to play it, but to an incompetent person it is no better than useless stones.”
“True--unless he sells it.”
[11] “We now see that to persons who don't understand its use, a flute is wealth if they sell it, but not wealth if they keep it instead of selling.”
“Yes, Socrates, and our argument runs consistently, since we have said that what is profitable is wealth. For a flute, if not put up for sale, is not wealth, because it is useless: if put up for sale it becomes wealth.”