Neck or nothing.
Taking a huge risk or making a great effort, often with everything on the line, to achieve a goal. It implies a "win or lose everything" scenario to proceed with complete abandon and recklessness, risking everything in a bold attempt for success.
The phrase comes from the sport of steeplechase racing, where a win by "a neck" was a victory, while not finishing or being far behind meant "nothing".
It's used to describe actions taken with a high degree of commitment and little regard for potential negative consequences.
Example: "Facing bankruptcy, he invested his remaining funds, going neck or nothing to save his business"
A steeplechase race
win by a neck
