I can't remember where I first saw this saying, but I remember I liked it and sort of latched onto it as one of those "Rules of Karate", if you will.
As karateka, we train in a potentially deadly martial art. Our art should never be used to harm someone out of anger or really for any reason other than dire self defense situations or times when others are in need of defense.
In the dojo we train to use "kime" or focus when we perform techniques with a partner. This is because our technique could really hurt someone if we actually hit them with it. If karateka hit each other full force in kumite practice, someone could go to the hospital or worse! In addition to kime, we also stress that people keep their anger in check and remember they and their partner are training together. It is not a competition and there is no room for an emotional response, no matter what.
Controlling emotions is also important in daily life. The stakes may not be as high as physical harm, but once a bridge is burned, it may not be possible to rebuild it.
As karateka we are committed to improving ourselves physically, but it is also equally important to have emotional "Kime" if we are to become really good at Karate.