A date written on the back can save a memory from becoming a guess.

Memory decays in a particular way: the feeling stays and the details go. You will remember the day at the coast without being able to say which year, which is fine until somebody asks and the answer becomes an argument between two people who were both there. A date takes five seconds to write and turns a family guess into a family fact. The person it helps most is usually somebody you will never meet.

Write dates on things this week. The backs of photographs, the inside of a book you are giving away, the label on a box in the loft: five seconds each.