Saïx didn't understand Demyx.
How hard could it be to obey orders just once? He didn't even have particularly hard assignments; take out a few Heartless, do a bit of recon, then RTC. The missions given to that new kid, Roxas, were harder than that! The difficulty of Demyx's assignments where slowly decreasing with each passing day, and still he managed to mess them up.
Saïx soon gave up assigning him to destroy Heartless, as he often left a world with more of the Dark monsters than it originally started with. He was eventually assigned recon missions, as it soon came to Saïx's attention that fighting really wasn't his thing. But even his recon tasks where a disaster. When he was asked to report back his findings, they would usually be brief bits of knowledge that anyone could tell you. It was obvious that no real thought went into his mission.
But it wasn't Demyx's incompetence that annoyed Saïx; it was his laziness. The blonde would avoid work in any way possible, and if he could find an excuse to not go out on assignments, he would use it. If Demyx had just put some effort into his work, Saïx wouldn't have be too bothered when he messed up. It was the fact that he didn't even try that made Demyx so infuriating.
