Metallic glasses are prone to fail mechanically via a shear-banding instability. In a remarkable paper Johnson and Samwer demonstrated that this failure enjoys a high degree of universality in the sense that a large group of metallic glasses appears to possess a yield strain that decreases with temperature following a -T2/3 law up to logarithmic corrections. In this Rapid Communication we offer a theoretical derivation of this law. We show that our formula fits very well simulation data on typical amorphous solids. © 2013 American Physical Society.