But many principals hire a mechanic because they have not the faintest idea whether the parts are in working order and a stockbroker because they do not know when it is best to buy, sell, or hold on to their securities. It is precisely because principals are incapable of contractual specification that many of them enter agency relationships in the first place. Moreover, as critiques of contingent-claims contracting assert, uncertainty and complexity make it costly, if not impossible-even for sophisticated parties-to anticipate all future contingencies and specify appropriate adaptations at the outset

Shapiro, Susan P., The Social Control of Imper…, loc. 48