There are some interesting comments here. I have some perspective that I'd like to share based on my experience riding horses for 11 years. The death of Jessica Forsyth is really tragic and from what I've seen in the videos on youtube, she seemed like an experienced rider who loved her horse. Sadly, some horses are just too overwhelming for some people like Boomer was for Jessica.
Based on what I've gathered from the events that happened on that day, Boomer sounded very hyper that day and kept evading the log. I think Jessica may have pushed him too hard that day. What made me realize is that trainer supervision is so important when jumping your horse. In the 11 years I rode horses, I NEVER jumped alone. Jumping is dangerous and you could get hurt... So you need people around to be there to help you in case anything goes wrong. Also, my trainers were very strict with me to make sure I was following the safety rules.
The most important thing to understand is that horses are very sensitive, alert animals, as affectionate as they may be. They are very tuned to their surroundings and they can react without warning when under stressful situations or feel uncomfortable. If you ride, you'll know that horses respond to cues given by the leg, heel, hands, and even your eyes and pelvis. They also sense fear very easily, even feeling the fear from the rider in the way she holds the reins.
So I've learned over the years that learning good horsemanship makes you a safer and better rider. The ultimate goal in training is for the horse to be calm and feel safe. When a horse feels calm and safe, a remarkable, trusting and lasting partnership can happen with his rider.