Death Note: Desu nôto2006

Ryuk:
Light, I'm gonna let you in on a little secret. What makes a shinigami and a human who has a death note different? Well, there are two things. And why do shinigami have to write the names of humans in their death notes? You got any ideas?

Light Yagami:
Of course not. Why would I know that? You know, you sure are talkative today.

Ryuk:
It's because we are able to take human lifespans for ourselves.

Light Yagami:
Huh? Wait. Whadda ya mean by that?

Ryuk:
Let's say you have a human who is due to live until the age of sixty, and a god of death wrote that this person would die at forty. Sixty minus forty equals twenty. Now those twenty years taken from someone in the human world are added to that god of death's life; so, it means that as long as we don't slack off - even if someone was to shoot us in the head or stab us in the heart with a knife - a god of death can not die. On the other hand, no matter how many names YOU write in your death note, your lifespan will not increase. That is the first difference between gods of death and humans who possess a death note.