|Normally when a character is hit, they suffer a short stagger during which they cannot act. This stagger also interrupts most actions, including attacks. GRIT allows an attacker to overcome this limitation for a short time.
Certain actions activate GRIT for a character. This can be identified by their body being wreathed in gold. While GRIT is active, the character will continue their action even if they are hit. Heavy Attacks with melee weapons usually activate GRIT, allowing the attacker to perform their slow and powerful attack even if a faster attack hits them in the meantime.
GRIT has limits, and can be broken through if enough damage has been dealt recently. Having a Heavy Equip Load increases the amount of damage you need to take before your GRIT is broken.
Most of the time, when you see a character glow in gold it's best to avoid whatever is coming rather than attempt to interrupt it.