The chief concern of every political society is the establishment of rights and of adequate securities for their protection. In America, it has been agreed that this shall be done by the people themselves; they shall make their own laws, and choose their own agents to administer them. But the obvious difficulty of doing this directly has been recognized, and the people, after formulating the charter of government, incorporating in it such principles as they deem fundamental, content themselves with delegating all powers of ordinary legislation to representatives. Notwithstanding this delegation, much direct legislation of a very effective and important nature is constantly going on, at the time attracting little or no attention. This is the steady modification of the common law by public sentiment, noticeable only when it has crystallized in general custom. The best of all laws for all countries are made in this way. Custom, when voluntary, is the conclusive proof of the final and settled conviction of the people as to what the rule of right and conduct should be on the subject to which it relates, and for that reason it is likely to receive spontaneously the obedience that statutes exact by compulsion.
Cooley, Thomas M. "Labor and Capital before the Law." N. Am. Rev. 139 (1884): 503-16.