Once you're hooked on reptiles. In fact, for many people, it's hard to keep any pet alone in any cage or environment. With reptiles, sometimes it's not only best to keep them separated, it's actually necessary.
Most reptiles are solitary by nature.
Typically, they share territories for breeding purposes, and only come in close contact with one another when necessary. They are not often interested in sharing their living quarters with another animal that, by nature, is considered competition. As a rule of thumb, however, your reptile in happier alone. His cage is his territory. Stick another reptile in with it and it might mean war.