Some historians spend years on one old diary. Going deep on one life can tell you a lot about a whole era.

One life contains a whole period in miniature, because a person has to live inside all of it at once. What bread cost, what was feared, who was trusted, what counted as a normal Tuesday: a diary carries that in a way a chapter about a century cannot. Depth and breadth turn out to be two routes to the same place.

Try it small this week. Find one letter, interview or diary entry from a period you are studying and read it closely instead of another overview. List five ordinary details in it, then ask what each one implies about everybody else alive then.