14 Issachar is a strong ass couching down between two burdens:

15 And he saw that rest was good, and the land that it was pleasant; and bowed his shoulder to bear, and became a servant unto tribute.

Issachar comes next, and he is compared to a donkey hunkering down between two heavy loads. From this, one thinks of qualities such as industriousness and perseverance. Whereas Judah was destined to be a nation of rulers and Zebulun a center of maritime trade, Issachar was destined for more earthy things. They are mentioned later for having their sheepfolds, and likely were farmers as well.

Though the pastoral life does come at a cost, as verse 15 describes. Those that work the land tend to be the ones that pay tribute to the ruling and warring classes. In other words, other tribes of Israel would have the courage and ambition to fight and lead, but Issachar would avoid the danger and choose to feed them instead.