Malcolm agrees to rent space in his mall to Zena for $5,000 a month. . Zena signs a 12 month lease, but departs after six months for a better deal elsewhere. Malcolm is furious. He gets an opportunity to lease the space previously occupied by Zena for $4,000 a month. Malcolm wants to gold out for six more months and charge Zena, but Malcolm's lawyer advises him to rent the space to the potential new tenant for $4000 a month. Malcolm's lawyer's advice is an example of :