Fights are over quickly
Most fights are over in seconds, not minutes. After a few punches, usually one of the fighters decides he or she has had enough, one of the fighters is incapacitated or knocked out, or someone separates the fighters. Whatever injuries that occur in a fight usually happen in the first few punches thrown. Remember the definition of a fight; it is mutual combat to determine dominance, so once dominance is established, the dominant fighter usually stops. Since fights are over so quickly, unless you have trained yourself repeatedly in using the techniques used in patterns and step-sparing, you usually will not think about using them in first few split-seconds of a fight or self-defense situation; you will just react instinctively and flail away in a mindless frenzy.
Fights are clumsy, awkward, and crude
Fights are nothing similar to competition sparring or the choreographed fights seen in movies. Even if the participants are trained fighters, the fight will not be pleasing to watch except for the excitement of the fight itself. You usually will not see beautiful, well executed techniques; just two idiots haphazardly flailing at each other.
When free-sparring, both opponents play by the rules. In demonstrations, the partner is cooperating with to ensure the technique works and looks exciting. In a fight, there is no cooperation and no rules, except for any unwritten rules of chivalry that may be observed.