Regarding protection and the use of same, the following are in my view relevant.
1. As the good Doc sez, the decision to use force is one of the most important one will ever have to make. The catch is, that decision must be pre-made. During the event is no time to be deciding if now is the time to smoke someone causing you grief. Your personal line in the sand must be pre-determined, as in 'If x happens, my response will be y'. Mindset, mindset and training are paramount if one presumes to survive an encounter of the potentially terminal kind.
2. One's choice of weapons will be in large part mission specific. That is, particular to your circumstances and the situations you foresee as being most likely. I would draw attention to the 'man with one gun' adage, but more than this, you must be comfortable with the device and be able to use it effectively, with little warning, and deliver force in an efficient way, thus improving the chances of stopping the fight before it really has a chance to get going in any kind of serious way. As with any other variety of social work, the personal touch makes a big difference.
3. Situational avoidance is of course the biggest defence any of us have. Not being in the fight in the first place will pay much bigger dividends than any rounds-per-minute ratings. Learning to live in Condition Yellow, at the very least, will enable the ready and timely identification of potential targets and the inittiation of the appropriate measures to deal with same. Avoiding such targets is first on my list, anyway.
4. Again, as the Doc so rightly pointed out, once the line is crossed, force must be immediately applied with maximum violence and minimum warning to the intended recipient. One is required to initiate hostilities in such a way so as to overwhelm the response options of the target, thus eliminating or greatly reducing the potential for retaliatory activity. It is difficult to get over the 'this isn't really ahppening to me' response, which costs precious seconds of reaction time, but it can be dealt with, which brings us to the subject of...
5. Training. Training, training, training. The US Army Rangers say that 'you will fight the way you train', and I have discovered this to be true. It is imperative that you practice with your devices of choice in a diligent, disciplined way, so that the actions required to run the device and keep it running during situations of dire need will be instinctive. Ideally, one must become 'unconsciously competent', as it is called. Failing this, one can at least be comfy with and intimately familiar with those devices.
All of the above begins with mindset.
I fervently hope the above has been helpful.
Diligentsia, Vis, Celeritas
Bailey