Cribbing. Bucking. Nipping. Rearing. Running away. There are so many things that our horses do that annoy or frustrate the heck out of us. Notice I didn't say "to annoy or frustrate" us - because horses aren't scheming or conniving against their human captors. They don't actually have the reasoning power to accomplish such a feat.
So, why do they do these things? The answer lies in both the science of equine behavior, and in a necessary re-adjustment of perspective in the horse-human relationship. It sounds complicated, but it's actually very simple:
The "problematic" things that horses do are usually very normal responses to abnormal living conditions and oftentimes unreasonable human expectations.
We often expect horses to simply know how to behave within our control, but that's an impossibility considering the abundant differences in brain processes, ethology (natural behaviors), worldview and learning abilities (among other factors) between our species.
For example, it's not possible for horses to understand why we've captured them and restrained them within 10'x 10' boxes, when the natural existence of a horse is to roam freely. In fact, such restraint makes no logical sense, once you know that a horse's digestion and other health factors rely upon locomotion. Unfortunately, most human horse handlers do not know this very basic fact, among others. And yet, we label horses that crib, weave, head-bob, or display post-inhibitory rambunctiousness after being let out of their stall as problematic. These so-called "problem behaviors" are the natural result of horse management practices that are poorly researched and a mismatch for the animals in our care - despite the fact that those management practices are considered standard (mostly because they are convenient for humans). There are SO many more examples, but they could probably fill at least a small booklet.
The point is, it is our responsibility as humans to learn everything we can about the horses in our charge. We're the ones who have decided to capture them and take them from their free-ranging lives, and while we are capable of scientific study of horses, the opposite does not hold true. In all sense of fairness, we should tailor our feeding, housing, daily management and training practices to the horse's natural patterns, rather than forcing them into our very human-centric paradigm. And when we do force them into our world, we should not expect them to cope without any adverse effects. It should be anticipated that there will be issues - such as the aforesaid cribbing, head bobbing, etc. However, it's far more humane to redesign the way we handle our horses, in the first place.
When we do encounter a horse that can't be caught, or paws a hole in their stall, or cribs, or bites, or whatever - we should be asking ourselves questions other than "what's wrong with this horse?". We need to consider key factors: does this horse have enough food and water? Does she have at least one companion? Forage? Freedom to move throughout the day? We have to take the horse's perspective and consider what needs might be unfulfilled and what frustrating circumstance might be causing the issue.
Because, in essence: there is no such thing as a problem horse. Just a normal horse living in abnormal conditions.