Why did the backpack feel overwhelmed?

This joke gets its chuckle from a clever bit of wordplay, specifically a pun. The phrase "carrying too much weight on its shoulders" has a literal meaning for a backpack, which, of course, physically holds books and supplies on straps that rest on a person's shoulders. But the humor comes from the second, metaphorical meaning: to feel burdened, stressed, or overwhelmed by responsibilities, much like a person might feel when they have a lot of emotional "weight on their shoulders."

The relatable context here is universal for anyone who's ever been a student. Backpacks are a staple of school life, and the complaint of a "heavy backpack" is practically a rite of passage. From lugging around thick textbooks to carrying all the supplies for a day of classes, students often literally feel the weight of their education on their shoulders. This joke playfully anthropomorphizes the backpack, giving it human feelings of being overwhelmed, which resonates with the often-stressful experience of academics.