One day, a young student came to Faust for advice and wanted to learn from Faust. Faust didn't want to be received, so the devil dressed up as Faust and answered all kinds of questions raised by students. Finally, he said, "Dear friends, all theories are gray, but the tree of life is evergreen."
This devil's words are often quoted by later generations. However, some people often use only half of it, or "the theory is gray" or "the tree of life is evergreen", which is inevitably biased.
Lenin wrote in "On Strategy Book": "Now we must understand an indisputable truth, that is, Marxists must consider vivid real life and the exact facts of reality, and should not cling to yesterday's theory, because this theory, like any theory, can only point out basic and general things at most and can only summarize the complex situations in real life. My friend, the theory is gray, but the tree of life is evergreen. "Lenin's understanding is very comprehensive and correct.