What makes a system good for self-defense?

This is such a difficult question and I believe there are not pat answers. Regardless, I will try my best to answer it from a very narrow perspective, i.e. my perceptions as to what it is that makes a system good for self-defense?

This answer does not contain specifics such as when this happens you do this technique or combination, etc. This is a very small part of SD training and practice but it does not cover all the bases. 

First, what is the systems syllabus? It is important to make sure a system for SD encompasses all the aspects involved in self-defense. It should address the before, during and after of any violent conflict. It must span from before you encounter it, while you are in it and then what happens after it occurs. 

Second, if must begin with what you need to know in order to recognize all violence. It must encompass those mind-set training that prepare the mind long before you go out and expect it to work. It must provide a solid knowledge of what violence is and how it works in all varieties. It all must be realistic.

Third, it must also allow for a reality based training and practice regimen that begins with the practice and training of what, when, how and why things lead you into conflicts. It must allow for the reality based training and practice that gives you the tools to handle things before you encounter conflict. It must allow for a reality based training and practice of what you need to accomplish when in a conflict zone and it must cover all the variables for that moment of conflict, i.e. each moment is unique and training and practice must address this. It must allow for a reality based training and practice for what you need to know, understand and do when you leave the conflict, i.e. the repercussions and after affects. 

Fourth, look to the instructor to see their history and experience. If they don't have a lot of experience or if their experience is within the system itself or if there is no experience in violent conflicts then look to their sources, look to their training and practice history, look to the same in their sources as well. 

If it fails to address the before, during and after; if it fails to address the mental/psychological, the spiritual, and the physical; if it fails to address the mental/psychological, legal and civil repercussions then your system needs further self-analysis to encompass all aspects of self-defense. 

It is too easy to drop into the particulars of SD including falling prey to the influences of advertisements and claims of any system. It is easy to succumb to the thrills found in all martial systems or any SD system. It is easy to fall prey to a perceived expert in a SD system.

Remember that SD is serious business. It has far reaching repercussions that will affect your entire life after, your families entire life after and your economic stability for your entire life after. 

In closing I want to say that this short terse post on what makes a good self-defense system is not all encompassing but rather a means to make you think long before you rely heavily on your local self-defense school. Buyer beware. The after of all SD is something you will deal with for a long, long time. Your ability to handle it before, during and after depend on your foundation of knowledge and experience. Failure to go the distance in your own behalf is your sole responsibility. If you fail to choose wisely you will have to look to yourself simply because you are the one choosing and deciding on your SD system.

p.s. as to SD systems, all systems have the potential to be good. All of them have the potential to be horrible. You can find a solid SD system if you do the footwork first and choose wisely. It could be anything and don't allow anyone to tell you one is either good or not good for SD, make that decision yourself.