To excuse compliance with a contractual term, “the impossibility of performance must attach to the nature of the thing to be done and not to the inability of the obligor to do it.” (Hensler v. City of Los Angeles (1954) 124 Cal.App.2d 71, 83 (Hensler).) Impossibility means not only strict impossibility, but also “`impracticability because of extreme and unreasonable difficulty, expense, injury or loss involved.'” (Oosten v. Hay Haulers etc. Union (1955) 45 Cal.2d 784, 788; see also Board of Supervisors v. McMahon (1990) 219 Cal.App.3d 286, 299-300.)
