“Obviously it cannot be open to every contracting party to act upon a bona fide, but mistaken, interpretation of a contractual document prepared by the other, and to hold the other to that interpretation. If an offer is made by one person to another, the offeree has to make up his mind about the meaning of the offer before accepting it and entering into a binding contract; once he enters into a contract by accepting the offer, he is bound by its terms, which (in the event of dispute) will fall to be construed objectively. Furthermore, even in the context of agency and other analogous transactions, the principle in these two cases presupposes, in our judgment, that a party relying upon his own interpretation of the relevant document must have acted reasonably in all the circumstances in so doing. If instructions are given to an agent, it is understandable that he should expect to act on those instructions without more; but if, for example, the ambiguity is patent on the face of the document, it may well be right (especially with the facilities of modern communications available to him) to have his instructions clarified by his principal, if time permits, before acting upon them.” 36. In other words, the critical question is not limited to whether the agent’s interpretation was reasonable; it is whether he behaved reasonably in acting upon that interpretation.”