Symbolism, Imagery, Allegory
Monsters, monsters, everywhere. Interestingly, almost all of Heracles' twelve labors involve monsters of various shapes and sizes. There's the Nemean Lion, the Lernean Hydra, the Erymanthian Boar, the Cerynian Hind, the Stymphalian Birds, the Cretan Bull, the man-eating horses, the three-bodied giant, and Cerberus (the three-headed guard dog of the underworld).
These monsters represent extraordinary violence, because they are lethal – they aim to kill. Not one is friendly. If Heracles doesn't kill them or beat them into submission, they will kill him. These monsters test Heracles' strength and intelligence. His ability to vanquish them says a lot about his ability to be a god or to be worthy of the gods.
We could also argue that these monsters represent the various challenges of life. The line at the DMV may not be an actual monster, but it certainly can seem like one. Final exams may not be an actual monster, but it may feel like a monster is to blame. These monsters not only test Heracles' athletic ability, they also test his brains, his heart, his determination, and his desire to achieve his dreams.