I think it's way more mature to realize that you no longer have the resources to do it all ( ie, take care of a pet and everything else) than to keep it and ignore it. Granted, turning it over to a shelter seems heartless, but is it more or less heartless to toss a dog that you don't have time for out in the yard or put it on a chain, where it can bark all day out of frustration and neglect, and then destroy things when it has the chance for the same reasons?