The goal of this paper is to provide background, heuristics and motivation for several conjectures of Deligne [12, 8.2, p. 163], [12, 8.9.5, p. 168] and [23, p. 300] and Goncharov [15, Conj. 2.1], presumably along the lines used to arrive at them. A complete proof of the third and fourth of these conjectures and partial solutions of the first two are given in [19]. A second goal of this paper i...