Humans are ritual casters.

With the discovery of new races and magics, it is learned that humans have ritual or chant based magic. This means that certain phrases hold power for all humans, but gain power when repeated with more people in unison, although some sayings are incredibly powerful by themselves and can be said by a single person, but across the realms all race have come to fear some human chants.

Sometimes entire battles halt when they see a line in the sand and hear "hold the line", or "and no further".

Bars across worlds dread the words "hold my beer" and "hey, watch this"

Regardless of weapons, duels are forfeited if a human utters "it's high noon", no matter what the time is.