You mention fatigue kicking in -- was it truly muscle fatigue or low blood sugar / bonking? From a lot of cycling I learned what it meant to, as the Dutch would say, "Meet the man with the hammer." Lifting at 430pm or so and relying on my lunch to provide the calories just wasn't good enough, I was starting to really feel drained half way through my squats. I recently added a serving of oatmeal and some fruit about an hour to two hours before workout and that helped eliminate that problem. Now when I feel like I'm hitting a wall, I know it's muscular and dovetails into what Brodie is talking about.
I wish someone had explained this to me earlier. I wasted several years of lifting by avoiding failure like the plague because I'd spent too much time reading Pavel's stuff. I had never failed a rep in the weightroom, ever, and had no frame of reference. He was probably preaching to the HIT crowd but I took the advice to heart.
When I finally did a linear progression, I realized I was had previously been lifting something like a 20RM weight for sets of five, with the corresponding lack of progress you'd expect. I eventually started missing reps every now and then.
When I started videotaping my workouts, I realized that the reps I had no legitimate excuse to miss the reps I did, given bar speed. It's been a slow learning experience, but coaching has helped immensely. When I started with Brent Carter I told him to let me know when I'm being a pussy. I'm pretty sure I needed that more than the form help.