Just Plain Stubborn...?
We've all seen them. Pictures of the overloaded mule or burro who either sits on its haunches or lies down; refusing to budge no matter what encouragement or pressure is applied to force its compliance.
Remember your Sunday School days and the biblical account of Balaam's ass? The donkey refused to move forward because it perceived the danger that Balaam was oblivious to. (Numbers 22:22-34)
Both instances could be seen as really stubborn behavior on the part of the animal. Don't forget, however, that the mule is a cross between a horse and a donkey and as such is highly intelligent; and, if treated with kindness, very willing to please. Since mules and hinnys have a lot of common sense and a strong sense of self-preservation this makes them resist situations where they might feel themselves mistreated or in danger.
Due to its keen hearing, eyesight, strength and endurance, as well as the inherent intelligence and the "fight or flight" instinct possessed by the mule, it might at times be worthwhile for the human to reassess the situation and try to see it from the mule's point of view. Your animal might actually know best and by his recalcitrance be trying to warn you of a potential hazard or even a fatal danger instead of just being plain stubborn.