Marriage, when it is genuine, is an identity merger — the self expands to incorporate the other as part of its own reference frame, and widowhood is therefore not simply grief but the shock of an identity that no longer has its organizing other. The widowed person is often asked, implicitly or explicitly, to reconstitute a singular self they may not have occupied for decades. The traditions that do this best tend to be those that provide both collective witness to the loss and patient time for the reconstruction.
Each step builds on the last.