Obviously if your basic assumptions or principles are not that smart, even if you go through advanced training you are bound to fail. The original Israeli Defense Forces Krav Maga explored the reaction time subject while many training systems did not.
So you will need more than learning methods or attack and defense or drilling them in motion, under stress and in different environment.
You need to take into account the worse case, when someone is trained well in using physical force with bare hands, or using weapons. You need to be able to respond to any tactical maneuver that your attacker might try.
One of the common errors in training is that the student in the attacker role does not do his best to challenge the defender.
It is not abut showing a better way to do an armbar, looking for a weak muscle, a pressure point, not even teaching how to prioritize when it comes to all options are on the table.
Or it could be a business owner that spend some time sweating in an office trying to find a way to falsify his way to a credible diploma in this field. Some did trained extensively in other martial arts, and some did not.
But they do need to understand what is a realistic approach and a proven method to bring someone quickly to master self defense and over come their business approach of only how to maximize profit and retain students.
Like boxing, fencing wrestling, Jujitsu match, it is very physically challenging and can become a great fitness activity especially with the extracted specific warm up to the muscle groups and the yoga extracted stretches prior to the class that helps prevent injuries in training.