A starving person who begs a crust of bread, is turned down, but takes it anyway is guilty of theft and has no defense. However, a person can take food from an unguarded cabin if starving in the woods.
This makes economic sense because of the transaction costs. In the first scenario there is a possibility to have a voluntary exchange whereas in the second scenario there is no such negotiation taking place because there is no party (thus, transaction costs are high). Transaction Costs in first scenario is lower than in second scenario because free negotiation is more likely in the first scenario than in second.