It can be somewhat «dark» to engage in self-defense training if you don't have the right mental attitude. It’s virtually impossible to practice self-defense without reflecting on the violence which surrounds us. Violence is negative and destructive, and it’s easy to become paranoid. If we take self-defense training too seriously, negative actions, thoughts and feelings can take over and change our lives for the worse.
Besides, most of us need an inner motivation to continue this kind of training. Fear of violence may cause us to start practicing self-defense, but not to continue training year after year. It’s therefore important to have a positive attitude towards the training. Don't take the training too seriously.
Also, remember that self-defense is about protecting yourself and those you love — not hurting others.
This is a short abstract from my book Self-defense by Jiu Jitsu. You can buy it on Amazon.