I disagree with this too. What about the person is working?
This is a big topic in itself and could be a thread. There are many facit of the person that are working. Two of the biggest are the mind and the emotions. If an individual does not/cannot work these two properly any technique he/she chooses will not work and that is not the fault of the technique.
The mind collects information from our senses and makes decisions based on this data. In a perfect situation this collection gathers 100% of all available information and the mind understands exactly what is occurring. In actuality this NEVER happens. Our past experiences and understanding of the world create a giant filter to help us interpret the world more quickly (not more accurately, more quickly). Likewise our emotions in the form of desires, fears, ego, etc., are an even bigger filter that further distorts our perception of the world and alters our decision making process. Training the mind and emotions for the least amount of distortion and the quickest decisions is what the person is working....or trying to work, whether they know it or not.
To get a better understanding of what I am talking about I suggest a book called "Deep Survival: Who Lives, Who Dies and Why" by Laurence Gonzales. It is not the quintessential work on the topic but is an interesting and easy read with loads of good information.
A quick example to further explain:
(Clarification: When I say 'you' in the following section it is the universal 'you' not a specific 'you.')
An attacker grabs forward with his right very quickly and it startles you for a fraction. However you have seen similar situations in your training and you know from experience your favorite technique is X. You are most comfortable doing technique X because you have the most success with this technique. You have a good understanding of technique X and an excellent mental picture of how to apply technique X and a good picture of the end result. Hence you are going to save yourself with technique X and begin to apply it. Now the attackers grab did not exactly match the training grab normally done for technique X but this is your best technique so adapt a little and go for it.
Unfortunately technique X works best off of a rear posture disturbance and the attacker is committed slightly forward. As you attempt to apply technique X you feel things are not right but hey this is your best one and hence your best choice, perhaps a little bit of strength applied just so will help or maybe a slight change in angle will do the trick. Now you feel the attacker resisting and actively moving. You still have this picture in your mind about how technique X looks when it is completed and you are attempting to make reality match that picture, after all this is your best technique. We can go on but you get the picture, I hope.
Our filters of past experience and our desire for a specific result can hinder us and distort our ability to make proper decisions. Clearly technique Y would have been better to start and once the situation changed slightly technique R was better or even technique E would have been good. You were stuck on X because of past experiences and an inability to truly see the situation for what it was instead of what you wanted it to be. I.E. People are effective or ineffective, not techniques. Change the attack a little and X is the way to go.
A technique is neither good nor bad, a person either understands how and WHEN to apply it or not. A person is the one that has the ability to perceive a situation correctly or not and continually adjust or not. The more stressful the situation the more difficult it is to perceive accurately and make proper decisions that match reality. In a very real sense this is can be a limitations of a technique based training system.
What is the mechanism in your training that challenges and develops the student's ability to properly perceive situations? What is the method of training you use to help students identify the emotions that distort perception and lead to poor decisions? Fear and ego have a huge distortion effect, how does your training method explore these effects and prepare the student?
Just some thoughts to chew on.