APAD:Jam tomorrow and jam yesterday, but never jam today.

Jam tomorrow and jam yesterday, but never jam today.

The phrase has come to be used figuratively to describe promises or situations where something is promised for the future or past but never made available in the present.

The expression originates from Lewis Carroll's 1871 book Through the Looking-Glass and What Alice Found There. This is a pun on a mnemonic for the usage of the Latin word iam (formerly often written and pronounced jam), which means "at this time", but only in the future or past tense, not in the present (which is instead nunc "now"). In the book, the White Queen offers Alice "jam every other day" as an inducement to work for her:

"I'm sure I'll take you with pleasure!" the Queen said. "Two pence a week, and jam every other day."
Alice couldn't help laughing, as she said, "I don't want you to hire me – and I don't care for jam."
"It's very good jam," said the Queen.
"Well, I don't want any to-day, at any rate."
"You couldn't have it if you did want it," the Queen said. "The rule is, jam to-morrow and jam yesterday – but never jam to-day."
"It must come sometimes to 'jam to-day'," Alice objected.
"No, it can't," said the Queen. "It's jam every other day: to-day isn't any other day, you know."
"I don't understand you," said Alice. "It's dreadfully confusing!"

usage example:

John Maynard Keynes, an English economist and philosopher  also makes use of the image of "never jam today" in order to portray vividly the tendency to excessive saving which may lead to economic stagnation:

For purposiveness means that we are more concerned with the remote future results of our actions than with their own quality or their immediate effects on our own environment. The "purposive" man is always trying to secure a spurious and delusive immortality for his acts by pushing his interest in them forward into time. He does not love his cat, but his cat's kittens; nor, in truth, the kittens, but only the kittens' kittens, and so on forward forever to the end of cat-dom. For him jam is not jam unless it is a case of jam to-morrow and never jam to-day. Thus by pushing his jam always forward into the future, he strives to secure for his act of boiling it an immortality.