Whose fault is it?

Theoretical situation 1:

You are tanking a pack of mobs with a clearly-defined kill order. A DPSer focuses on your primary mob but his AoE pulls aggro from another mob, causing his death. Whose fault is it?

Theoretical situation 2:

You are tanking a single mob. A DPSer manages to pull aggro from you and dies. Whose fault is it?

Call me wierd weird, but in both cases, it would be my fault, unless the DPSer massively outgeared me, or I was having latency issues. In a perfect, lag-free world, yes, the fault would be mine first and foremost, and the DPSer's second.

Let me explain. In situation 1, it would clearly be my lack of situational awareness that caused me to have insufficient threat on the particular mob that killed my DPSer, while in situation 2, I must have been dreaming or thinking about lunch or something to that effect. Allow me to clarify that this is a more radical, new-school style of thought. The old school of thought (prevalent back in TBC) is that as DPSer, you watch your own threat; if you overaggro and die, its your fault. However, I suppose this is close to impossible now.. monitoring your (DPS) threat on the primary AND secondary targets (think Whirlwind or Divine Storm).

I suppose its this chain of reasoning that constantly makes me strive to put out more threat (read: damage) so as to allow my DPSers to perform at their maximum capacity.

Now, I will admit that both situations have happened to me before, either via mispulls or having my mind wander. There even have been non-fatal occurences of the second scenario. What I'm saying is... Nobody is infallible. But if you can learn from your mistakes so that you can become a better tank... Everybody benefits, right?