Opportunity cost
From DominionStrategy Wiki
Opportunity cost is the lost benefit of not buying one card in favor of another. For example, a "village idiot" would continue buying Villages when he could be buying Silvers, so when he does not have enough buying power for better cards, he can blame himself for not considering the opportunity cost of buying Villages over Silvers. In another example related to buying power, a Hoard buy could have been a Gold buy instead, so if you get a hand of Hoard-Silver-Copper-Copper-Copper as the game is nearing its end, you may rue the opportunity cost of buying that Hoard instead of a Gold, since is needed for a Province.