like nailing Jell-O to the wall

like nailing Jell-O to the wall

Incredibly difficult or impossible, such that it could be seen as a foolish or worthless endeavor to attempt. (Jell-O is a brand of gelatin-based deserts, which are known for being wobbly and unstable.) Trying to have a reasonable debate with her father is like nailing Jell-O to the wall. If they can't secure a victory here, climbing back to spot in the finals will be like nailing Jell-O to the wall.
See also: like, nail, wall