This is an obvious question with what seems to be an obvious answer — why do we get bored?
Actually, it’s not that simple. Researchers are studying how and why people get bored, and what the implications are. For example, our economy would be much better off if everyone were fully engaged in their work.
So why do we get bored? Perhaps it’s an economics question — you know, about the allocation of scarce resources. If we’re bored, perhaps our talents are being wasted on whatever we’re doing and could be better used in some other way? (Which implies the average elementary-school student is a budding economist!)
To pursue this further, there is an excellent podcast about this on Freakonomics Radio — http://freakonomics.com/2015/10/29/am-i-boring-you-a-new-freakonomics-radio-episode/