[philwelch]

There's a plausible case that advertising is a negative-sum game (in the game theory sense). If no one advertised, they wouldn't be worse off since we would still buy the stuff, but if one player defects and advertises, they gain an advantage so the Nash equilibrium involves wasting lots of money on advertising to no net gain.

[kbutler]

The best advertising educates the receiver, rather than just trying to persuade to buy one product over another.

Advertising can thus be a positive-sum interaction.

Unfortunately, it's usually easier to target the other product, rather than promote one's own (see political advertising).