It's possible you're thinking of the opposite: "mind over matter."
Mind over matter is a common idiom that means believing you can achieve something even when it seems physically impossible. It suggests that willpower and mental strength can overcome physical limitations.
Examples:
* "She managed to lift the heavy box, a true testament to mind over matter."
* "The athlete pushed through the pain, demonstrating the power of mind over matter."
If you were referring to a different idiom, please provide more context or the full phrase.