Reiatsu

Firstly, no two Reiatsu were the same. Not even twins had the same Reiatsu. Secondly, someone with a powerful Reiatsu could completely crush someone with a weaker one without even having to use their weapons.
If the difference was too high, the one with the weaker Reiatsu could collapse, faint, or even die depending on how much power was used.

-Gojo CH 11: TEST (2)