I disagree with this post here.
This isn't always true.
If a healer dies it could be the Tanks fault , it could be the DPS fault or it could be the healers own fault.
In the Athiss station the last boss has dot that does a crap load of damage to anyone who gets it. The person will most likely die if the healer doesn't heal the DPS or himself or remove the debuff. If you wanted to place blame then I would say its the healer fault.
If the tank pulls a crap load of mobs and the healer can't keep him up then its usually the tanks fault. If a DPS pulls mobs while the tank is AFK and the healer dies because of it, then its the DPS fault that the healer dies.
What caused someone to dies depends on the situation. If you can't put the mental effort into figuring out what is causing people to die other than some made code to live by then you will have a hard time progressing.