I've worked with my friend helping out in his business for years on call outs when he had the council contract etc etc. It wasn't until last year that i choose to do the CS30 course but then i never picked up a saw before hand as I'm not one to use equipment without proper training.
I have common sense and apply it all the time. I just feel that if you have common sense then you can also be blinded by it and feel as though you are doing things correctly. I have a healthy respect of all power tools, equipment that brings a high risk of serious injury. I apply the same to weapons. It's not the equipment it's the person behind the equipment that is dangerous. I've taught countless new recruits weapon handling skills and the correct and safe way to use a rifle, yet i would not pass them on there weapon handling skills as they are still dangerous in my eyes and would not take them on the range. Some people just don't have the skill for manual handling of tools/equipment.
It's the same for electrics. I know i could do the job, but choose to call my mate who is a qualified electrician to carry out the work in a safe manner and have peace of mind that the job has been done as safe as possible.