Your spirit and resolve are completely indomitable. It could be for any number of reasons, but the result is you do not, under any circumstances, voluntarily back down, give up, surrender, or retreat, despite all odds. While some might consider this a boon, most people know that there are many circumstances in which one might need to run away. Your incapability to retreat will cause all sorts of misadventures for your allies — that is if they don't leave you behind.
If you are compelled to run away from failing a Guts check against a magical or supernatural effect, however, you may turn your tail and run, though you'll despise yourself afterwards.