The commandment was sufficient.All conceptualization is based on known factors. Everything we have ever imagined has a basis in reality. We cannot create out from nothing, only God can do that. In order for Adam to comprehend death in any way, the Lord would have had to use some form of reality. A dead animal, a skeleton or even a dead leaf would have sufficed to teach a concept that death is a bad thing. What do you think the Lord could have used in the garden of perfection??