Fights may be brutal
Some fighters are experienced and ruthless. They may gouge the eyes, bite, use broken bottles, or even use knives. When it comes to a fight or a self-defense situation, feints, fakes, footwork, etc. are practically useless. Things will be happening fast with no breaks in the action; you just do what you have got to do as quickly and effectively as you can do it. If you enter a fight, even if you think it is just a friendly fight, you must be prepared for the worst, which means you must be prepared to be ruthless if necessary.
It is easy to say you would do whatever is necessary to defend yourself, but, when the time comes, it will not be easy to do, unless you a have done it before. Many of the techniques you learn in patterns and step-sparring are actual brutal blocks and attacks. They are not to be used indiscriminately; they are not something to be used on playgrounds or in simple bar fights.
Fighting is not free-sparring, it is not completion fighting, and it is not self-defense. It is mutual combat for some personal, usually trivial, reason. While fights usually end quickly with little serious injury, they may escalate into brutal life or death situations, so take fights seriously and avoid them whenever possible.