Gordian Knot
An exceptionally difficult or tangled problem, named for the ancient story of Alexander the Great and an intricate knot.

Context
In the legend, the knot was associated with a prediction about the person who could undo it. Alexander the Great is famously said to have solved the challenge by cutting through it.
To cut the Gordian knot now means to resolve a stubborn problem through a decisive move that changes or bypasses the terms of the puzzle.
Examples
- A project might cut its Gordian knot by replacing an unnecessary approval system that keeps every small decision stalled.