Self Taught

Glory had, in her time as a superhero, dealt with aliens, super-soliders, wizards, even an alien super-solider wizard that one time.

But fighting herself, or at least an alternate version of herself, that was new. And unfortunately, her other version was equipped with powerful weaponry.

Glory found herself on her back, trapped blocking her other self's blade, her shield breaking as Glory looked into her other self's eyes and... Saw a lack of a scar on her eyebrow.

So her other self never fought The Merc? And thus never learned an important lesson.

When in doubt, go for the eyes.