Qin Mugong asked Bole to recommend a successor. Bole said that Jiu Fang was worthy of the job. Jiu Fang was out of Mu Gong's order to find a horse, and after three months he revived and said that the horse had been found. Mu Gong asked: What is it? Jiufang replied: The yellow stallion. Mu Gong sent someone to fetch the horse, and the horseman reported that it was a black mare. Mu Gong was displeased, and he was responsible. How can you tell if it is good or bad? Bole replied: "If you look at it, there is also an opportunity. It is so fine and forgets its rough, inside and forgets what it sees. See what it sees, not what it doesn't see; see what it sees, and leave what it doesn't See. If the person who looks at you is a horse, there is something more expensive than a horse. "Ma Zhi, a horse of a thousand miles. What is the main point supported by this passage? ['Maxima cannot be distinguished by horse color and gender.', 'Horse color and sex are key to discrimination.', 'The nature of things is determined by their internal causes.', "Seeing what he sees and seeing what he doesn't see is the key to understanding things correctly."]