The fact remains that to get very good at an art like Kenpo, it takes practicing multiple hours a week, week after week, month after month for years. Now, when you weigh the actual likely risk that you will be attacked (the sort of attack that would require hundreds or thousands of hours to defend against), which is typically very slight, versus the amount of time most people spend training in arts like Kenpo, that is not a very rational procedure if your goal is merely strict self-defense. In sum: huge investment of time (thousands of hours of your life) for a scenario that will likely never occur. In almost any other endeavour that would be labeled "insanity."