“The fundamental tension of the profession is the struggle between bold advocacy of the client's interests and the need to establish and hold to limits that prevent advocacy from leading to irrational and inequitable results; and thus the lawyer's job in practice is to be on one hand the impassioned representative of his client to the world, and on the other the wise representative to his client of the legal system, and the society, explaining and upholding the demands and restrictions which that system places on them both. ”