“Jam tomorrow and jam yesterday—but never jam today.”
The rule is comic because its promise is permanently deferred: reward exists on every day except the one a person is actually living.
Source details
Through the Looking-Glass, Chapter V, “Wool and Water,” printed page 94 / scan leaf 114 in the fully validated 1872 Macmillan first-edition witness on Wikisource. The White Queen explains the impossible rule “jam to-morrow and jam yesterday—but never jam to-day,” a linguistic joke about living backwards and “every other day.” It remains fictional nonsense logic rather than practical advice about delayed rewards.