Albert Henrichs, "Mani and the Babylonian Baptists: A Historical Confrontation," Harvard Studies in Classical Philology
77 (1973) 23-59 (at 59):
Written records are the raw material of past history, especially for the modern historian who would be at a loss without them. But in the field of ancient religious beliefs and movements, perhaps more than anywhere else, the very lack of sufficient documentation tends to call forth a rather disproportionate amount of scholarly activity, doubtless nourished by the tacit conviction that when we deal with Geistesgeschichte, certain invariable features of the human condition entitle us to substitute assumptions for recorded facts. What usually comes up in the rear of such forced advances into unknown territory is a large array of conflicting theories, from which scholars choose or to which they add, according to their likes and dislikes. Unmapped areas in the history of the human mind thus become the training ground for our imagination, and rightly so, as long as there are neither reliable roads nor signs to follow. With every piece of new evidence, however, an increasing sense of direction develops. Thus many a long vagary has come to an unexpected end after the discovery of major documents which opened new vistas. But it would be impossible to think of any written text which has come down to us, however well preserved and rich in information, that has solved all our problems. The triumphant feeling which great finds inspire, more often than not, gives way to a more disenchanted attitude when we come to realize that ignorance is the toll of historical truth and that behind each foothold in newly gained terrain, looms an abyss of nowhere. After we have pitched our camp in the new location, we are once more left with conjecture and imagination as our only guides.