you can't get a quart into a pint pot

alternative you can't fit a quart into a pint pot · alternative you can't put a quart into a pint pot

1. literallyYou cannot fit a large object or amount in something smaller.
2. figurativelyOne cannot achieve the impossible.

   They've asked me to get from London to New York by five o'clock, but it's half past four now, and you can't get a quart into a pint pot!

   1 more example

   The centenary of Britain's most famous train has called for a commemorative and descriptive work and in this 40-page illustrated booklet the author has tried—with some success, to pour a quart into a pint pot.

   1962 October, “New Reading on Railways: The Flying Scotsman 1862-1962. By C. Hamilton Ellis. Allen & Unwin. 6s.”, in Modern Railways, unnumbered page