Another good point. It looks almost like a symbiotic relationship, our Digimon get something out of us, and we in turn can get something out of them. For the Digimon, that looks like a way to get to their higher forms; or at least, for the first digivolutions I've been around for, the digivice lights up when we the partners are in need, the Digimon doing it for us. Whatever the digivices are, they seem dependent on the relationship between the person and their Digimon.