I've seen a lot of people that are confused or even angered by the event that have progressed in world of warcraft concerning some of the 'cannon' lore. Prince Kael'Thas Sunstrider for instance.

Generally Kael was a caring, if a bit arrogant, kind of guy. After the Scourge attacked his people he took charge and assumed command over the survivors. That, of course, was back when Quel'Thalas fell and the high elves renamed themselves blood elves.

This is the turning point for good old Kael. Undead hatred and a severe hatred for the alliance since he felt they had failed his people. Plus compiled onto that his people now had nothing to feed their addiction to magic since they had lost the sunwell.

After the sunwell incident he joined, reluctantly, with Warden Shadowsong and High Priestess Tyrande to hunt down illidan. In a long and conveluted process he ended up using the Naga for help twice which got him repremanded and then thrown into the dungeon of Dalaran, where he had spent a good portion of his life. Lady Vashj freed Kael'thas from the dungeons and helped him escape to outland where Illidan was waiting. Illidan convinced Kael that he could help with his peoples' addiction so Kael signed on.

Illidan, still on the bad side of Kil'jaeden, was forced by his former master to try and destroy the frozen throne. During this time Kael attempted to thwart Arthas' attempts to get to the frozen throne first. Arthas defeated Illidan, so Vashj and Kael retreated back to outland.

The burning crusade picks up with the blood elves trying to reach outland to reunite with their leader. However, with Kael's loyalties changing and his allegance with Illidan eroding not even his own people want to side with him.

So that's what addiction and a hard life will do to you. With this in mind, do you really think that you could have persevered and forged on better than someone as mighty as Kael'thas? Further more if you own the cannon, can you actually deviate from it or are you just progressing the story?