[I]t is the transformation of custom into customary law—into something that State courts will recognize, enforce and require—that disrupts the continuity of the indigenous systems. In pre-colonial times … [the settlement of disputes] … depended … on the mutual processes of negotiation and compromise. There is no need to romanticize these processes…. But the important point in this context is that norms play a very different part in negotiations to that which they play in legal processes. They may be used to stake out negotiating positions as a starting point from which to proceed or as a sounding board as to the correct procedure in the cultural and symbolic sense, but they cannot be cited as rules or conditions that will be imposed.1