Unknown Unknowns

Since I stopped watching TV, among other topics, I’ve been reading histories of the ancient world. In The Spartan Regime,Sparta Paul A. Rahe writes, regarding evidence of the past and how to understand it:

… scholars find themselves in the position of children eager to reconstruct a vast jigsaw puzzle—who are aware that the great majority of the pieces are missing and that many of those which have survived are broken, and who then discover, to their great dismay, that their situation is complicated by yet another, perhaps even graver deficiency: for they have not the vaguest notion what the puzzle would look like if they actually managed to piece it together.