[clavalle]

Transactions cannot be zero sum. What would the point be?

In the common case: Two people come together and trade because each feels they get more value after the transaction than before the transaction. Positive sum.

In a less common case: Two people get come together and trade because without the trade one of them would lose more than the value they spend on the transaction and the other one gains value. For example, if you have a gold watch but you are hungry and have no cash and I have food you might trade that watch for a sandwich. Also not a zero sum game. In this example a negative sum but I could imagine a positive sum where the one party gains more value than the other stands to lose after the transaction is complete. Say, you need to pay some workers on your construction crew and you have a generator that is normally worth about $50K and you sell it to me for cash at $40K. I, in turn, use that generator to do my job worth $100K that I wouldn't be able to complete without it..etc. It can get complicated.

A zero sum transaction would have one person losing the exact value the other person gains. A very odd and rare case I would guess.

[dredmorbius]

Transactions can be negative sum.

Theft or armed robbery are transactions. They typically reduce overall wealth.

[meric]

Also gambling between two people - though one party loses the exact amount the other person gains, the time spent to place the bet and to watch the result costs time. One could argue they both gained utility in terms of enjoyment, but in terms of wealth and GDP the transaction is negative-sum.

[monort]

By this logic any entertainment-related transactions are zero-sum. People gain utility by being entertained, sometimes you can even objectively measure it, e.g. higher productivity after holidays.

[dredmorbius]

Note that you've made the leap from "may be" to "must be".

There are numerous highly persistent behaviors, including play, entertainment, sleep, drugs consumption, recreational physical activity in excess of all training response stimulus requirements, etc., which nonetheless continue.

While I'm not certain that all are beneficial, and I have a difficult time myself accepting certain of these, I suspect they play a useful and possibly even vital psychological role for those undertaking them.

Even explaining these as coping mechanisms for underlying pathologies isn't particularly satisfying.