It's one of the weird ironies of life that our feelings are often at their biggest when we're at our smallest. Sure, grown-ups have been known to have the odd tantrum as well, and they can be pretty scary — as in incidents of road rage, for example, where drivers have pent up feelings of frustration they can't overcome.
It's all about managing emotions. Toddlers generally haven't picked up the skills to manage the feelings they're just starting to even recognize, which is why they have those outbursts.
Grown-ups and toddlers alike might have something to learn about managing their big feelings from one six-year-old who's become a viral star.