What do you think is the most difficult word to write?

I think the most difficult word to write is "straight to the point", which I overheard a classmate say when I was in middle school, referring to the difficulty in calligraphy. The main idea is that the strokes of these four words are simple, but profound. Calligraphers need a strong foundation to write a profound charm with simple strokes. But now, I haven't found an introduction to these words on the Internet, but I know that these words were originally used to describe the vigorous brushwork of the ancient calligrapher Wang Xizhi, and now they are mostly used to describe the profound and accurate viewpoints and arguments. (The language "Shuo's Clans" Volume 87 quoted Zhang Huaiguan's book "Broken Wang Xizhi" in the Tang Dynasty: "Wang Xizhi's book is a blessing book, which is carefully cut and incisive. )