1. Most people who suffer from low back pain lack hip and thoracic spine mobility. Typically when a joint causes pain. The problem isn't in the joint itself, but the joints above and below. For example, the lumbar spine isn't meant to be very mobile (only about 15deg of rotation and very little flexion/extension). When a person lacks mobility in the hip and t - spine, the body will compensate by increasing mobility in the lumbar spine. This is causes undo stress to the joint and it becomes inflamed.
2. People need more anti rotation and anti extension work. This is also a major cause of low back and knee pain. Without a strong "core", the spine will have to bare most of the stress on the body. This isn't good. Do more planks, bridges, rollouts, and pallofs.
3. It's all in your head. I just read this article on Tnation, and it really goes along with the things my training partners talk about all the time. Mind games. Many people will quit mentally before they quit physically. For example, when doing a heavy yoke walk or walking a heavy squat out of a rack, it literally feels like the weight is CRUSHING you. The trick is, to have that feeling of THAT weight on your back and not care.
4. Bad programs, not bad exercises. I didn't come up with this term. I can't member who did. But, it can be applied to anyone who asks questions like: Is squatting going to hurt me? Benching? Crunches? Here's how I answer: If you have poor hip mobility, don't squat. If you have extremely long legs in relation to your torso (basketball players) don't squat. If you find your self in the seated position for most of the day, don't bother with bench or crunches. Simple enough?
There you have it. Sorry, I know 4 is a weird number. I'm out of time. Gotta go make some kids faster!