There are several myths about Martial Arts that are propagated as the truth by people who like to attract a lot of students and then teach them very little of any use.
This is nonsense. Martial Arts do not teach anything. People teach people. Martial Arts is a framework which describes a body of knowledge about the subject of fighting. If the teacher knows nothing then they will not be able to teach anything of any use. If the teacher cannot fight then his knowledge, no matter how vast is of no practical use whatsoever.
Respect is earned, it is not taught. Teaching somebody to bow to the dojo, senior students, the master etc does not teach respect. It merely teaches a method of enforcing a hierachical structure based upon longevity rather than ability. This leads to the situation where the superior fighter must respectfully not beat a higher ranked opponent and must respectfully be flattened by his teacher with the wave of his Qi imbued aura.
The only real discipline is self-discipline. People who have to go to a class to train and do not practise alone to hone their skills lack self-discipline. They fool themselves they are being disciplined by the fact they turn up to the classes once or twice a week, but only train hard under the scrutiny of their instructor. They will stand in line and perform the perfect punch a thousand times in time with everybody else. This looks like discipline but it is a special kind of enforced discipline which very quickly evaporates when not in the context of the activity. One only has to note the behaviour of ultra-disciplined soldiers when they get out of uniform.
Self-Defence is a marketing ploy to get people who do not want to fight or train to spend a lot of money to learn a few tricks which will supposedly save them in a life-threatening situations. The chances of anybody who has learnt a few of these tricks without the many hours honing them to a level where they are practical and can be done without thought is practically negligible. Fortunately most people who learn this stuff never have to put it to the test. It can however give them a false sense of security and can actually be more dangerous to them when their assailant is annoyed by their failed self-defence technique.
The art I practise is called Practical Tai Chi Chuan, which gives equal emphasis to all aspects of the art including the art of Tai Chi fighting. There are those who have never fought and have only learnt the "applications" one at a time so have never had to put them together or attempt to use the Tai Chi fighting strategies. These people then claim that Tai Chi is only good for self-defence against untrained people and that it cannot be used against trained fighters. They even misunderstand the term "application" which is of course just a practical demonstration of a principle. They mistakenly believe that this is the only way the move should be done , rather than a general principle to approach a certain type of movement.
Of course what they mean is that the way they practise and teach it means that they and their students would not be able to survive against a trained fighter. Instead of accepting the limitations of their own understanding of the art and the inadequacy of their training methods they will make catch all statements about the art itself.
If you really want to be able to defend yourself against anybody it is necessary to learn how to fight and not just learn a number of "techniques" against a set of unrealistic scenarios. The theory is meaningless without the practical application of the ideas in unfamiliar and stressful situations.
Those who have never fought using the Taijiquan method will never understand this and their art will remain empty.