The answer is: first crisis of life, trust versus mistrust.
According to erickson's trust versus mistrust, at some point people would experience a period of time when experience an uncertainty on whether we should trust the caregivers around us to help us survive in the environment.
For most people, this crisis happened between the age of 0 - 2. If, this crisis is not solved within those age , it might resulted in further complication as we got older. Hoarding behavior that displayed by the roommate could be interpreted as a result for this unsolved issue