Briefly introduce the story of Yan Zhenqing calligrapher's hard practice of calligraphy, about 25 words.

Zhang Xu told him: "If there is any' secret' in learning calligraphy, it is to study hard and practice hard. Remember, people who don't work hard won't achieve anything. " Yan Zhenqing was greatly inspired by his teacher's teaching, and he really understood the learning methods. From then on, he studied hard, studied hard, learned the charm of calligraphy from life, made rapid progress, and finally became a great calligrapher, ranking first among the four calligraphers.