"Kunzi writes very well" is usually a compliment to a person's calligraphy, which is very beautiful, neat and beautiful. Kunzi refers to Chinese characters with certain difficulty, which is difficult to practice in calligraphy. A person can write a good Kun character, which shows that this person has a very solid calligraphy foundation and a high aesthetic level.
Sometimes it may be to remind that person to work harder on calligraphy. A person who writes the word Kun well can further see his love and devotion to calligraphy.