“How can the light of day know how dark the night is?” It means that the light of the sunrise during the day, how can it know how dark the night is? It means that people's cognition is limited and it is difficult to understand completely different realms. It is similar to "summer insects cannot speak of the ice" and "frightened frogs cannot speak of the sky".

"The light of day does not realize the depth of night" comes from a landmark work "Suluchi Sayings" by the German philosopher and thinker Nietzsche, or translated as "Thus Spoke Zarathustra" 》. Original German text:

"Wer sich tief wei?, bemüht sich um Klarheit; wer der Menge tief scheinen m?chte, bemüht sich um Dunkelheit." - Friedrich Nietzsche, Die fr?hliche Wissenschaft

The meaning of this sentence is - it means that it is difficult to know the depth of the other party if they are not in the same position. Later, it was quoted by the famous Japanese writer Haruki Murakami at the end of his work "Hear the Wind Sing", in which the fictional writer Hatfield was created. According to his will, his tombstone quoted Nietzsche: "The light of day does not know the depth of night."

Extended information:

Publication background

During World War I, two books were most common in the backpacks of German soldiers heading to the front line, one was the Bible and the other was Nietzsche's "Thus Zarathustra" explain". The influence of Nietzsche's ideas on power on Hitler is also well known.

Nietzsche's "Thus Spoke Zarathustra" incorporates the essence of his lifelong philosophy, is full of passionate thinking and exploration of the pursuit of progress and independence in life, contains positive wisdom, and is not lacking in the beauty of human nature. The bag is permeated with philosophical speculation and the poet's passion, leading people to spiritual nobility, inspiring the fighting spirit of self-improvement, and gaining a deep understanding of life, without the tragic consciousness and excessive melancholy revealed in Nietzsche's other works, his paranoia, and arrogance Waiting doesn't seem to matter anymore.

"Thus Spoke Zarathustra" occupies a special place. I have given mankind an unprecedented gift with this book, and the voice of this book will resound throughout the ages. It is not only the tallest book in the world, the truest book of the mountaintop—with the whole phenomenon and humanity far below it—but it is also the deepest book. It springs from the richest truth, an inexhaustible source, so full of treasures that it is easy to put down the bucket.