User blog comment:Godisme/Deicide 20/@comment-1268838-20100902031559

Asides from "plan," Aizen's favorite word is "understanding." He was always calm and collected because he understood the way things around him worked. Because of that, he always knew exactly how to deal with the issues before him - as you said, he strength was in his intellectual ability. This included an understanding of his own limits - by understanding them, Aizen knew that he could surpass them.

And so he subdued the Hogyoku - what we see here seems to be an Aizen blinded by power, a being that believes that he has transcended the world of reason. He no longer needs restraint, because nothing could possibly oppose him. Or so he thought. Here we have Ichigo, the one wild card in Aizen's pet project. But there's a problem - he doesn't understand him. For the first time, he's facing an opponent that isn't fazed by his words, that doesn't crumble at his very presence, that doesn't show overt caution or hesitation against him. This is something outside of his realm of thought - for once, he doesn't understand. A lack of understanding tends to birth fear - a fear that his power isn't all that he hoped it would be, a fear of being inadequate after all he has gone through, and moreso, a fear that he has miscalculated Ichigo Kurosaki. We have never seen fear in Aizen's eyes before - wanting to prove contrary to all of this, Aizen flaunts his power, desperate to erase this enigmatic obstacle, only to fail.

All in all, Ichigo is scaring the living crap out of Aizen; he never saw this coming by a longshot.