These impediments are elements of our personality that we identify with and which keep us from seeing the "void" within our being. People will probably easily understand how fear, greed, lust, gluttony, etc, obscure the mind and get in the way of the interior life. But the book goes beyond these obvious problems and identifies other issues.
Take the example of one of the masters who finds himself beset with the following vision while sitting and forgetting.
---a young girl stood in front of him. She was dressed in rags and her arms and legs were covered with bruises. Ch'iu Ch'ang-ch'un heard her say, "Kind sir, please escort me to my uncle's home. My stepmother has beaten me and turned me out of the house. "--- ---Ch'iu Ch'ang-ch'un acted as if nothing had happened. The image of the girl disappeared and his sister-in-law appeared saying, "your elder brother died of an unknown illness, and your uncle has taken over your father's property. He has given us three days' notice to leave. My children and I have nowhere to go. Come back quickly and put things right." At the same time, Ch'iu Ch'ang-ch'un's nephews and nieces appeared, tugging at this sleeves saying, "Uncle, please come home. Our father is dead. We will all be beggars if you won't help us." Ch'iu Ch'ang-ch'un continued meditating. The images of the children and his sister-in-law disappeared. Soon after that the fog lifted. (p 145)
The obvious point is that we are blocked not only by our attachment to "negative" emotions, such as lust and greed, but also by "positive" ones like love and filial devotion.
I should point out that the author is not just talking about the mental images and hallucinations that one sometimes has while doing "sitting and forgetting". There are other significant examples. The head teacher, Wang Ch'ung-yang, goes to visit the village where he used to live and finds out what happened when he wasn't there. (Just like in the movie "Its A Wonderful Life" when the angel shows George Bailey what his town would be like if he had never lived.) Wang had defended the poor and been a significant force for good in his town, so when he left it to become a Daoist it totally fell apart. Moreover, his wife was so upset and distraught that she died of grief a year later. Yet Wang doesn't have any regrets about his decision. His detachment is complete.
These two examples hit very close to home for me. Indeed, I literally do have people from my past---like the bruised and beaten young girl---who come to my door pleading for help. Moreover, I concerned about the fate of the earth and the people who inhabit it. (Indeed, out of habit I turned on the radio to listen to Democracy Now in the middle of creating this blog entry. It took a real act of will on my part to turn it off and go back to writing.) If I had been in Wang's shoes, I would have been devastated to come back home and find my town destroyed and my significant other dead.
These elements of our minds are very subtle. They "creep up" and put you in a very difficult space. The character Ch'iu Ch'ang-ch'un goes through a period in his life when he progressively becomes more and more obsessed by the prediction of a fortune-teller that he will die of starvation. He eventually decides that he will simply starve himself to death to get it over, but a group of bandits find him and actually force food down his throat against his will in order to keep him alive. Eventually, Ch'iu decides to end it all by hanging himself with an iron chain. At that point one of the Star immortals takes on the appearance of an herb gatherer and talks him out of it:
So you wanted to die after listening to one man's words. Maybe another man's words will bring you back to your senses. Your mind is invaded by monsters, and your wisdom is clouded. Your folly has not only almost taken your life but also ruined your chances of becoming an immortal in this lifetime. Listen to what I have to say, and the monsters who have captured your mind will leave you. (pp 138-139)
And once Ch'iu Ch'ang-ch'un listens to the herb gatherer and understands, he realises the error of his way. But pay attention to what the gatherer says when Ch'iu offers his gratitude:
You need not thank me. I did not give you money or food. I only uttered a few words. It was up to you to believe them or not. You liberated yourself from the monsters of the mind by realizing that it was your folly that trapped you into your preoccupation with death.The point is that the only person who can free an individual from their obsessions is themselves. The monsters of the mind are created by ourselves and can only be destroyed by ourselves. Moreover, many of the problems we face are the result of these delusions instead of objective forces beyond our control. For example, the people in Wang's village did not have to fall into chaos after he left. Nor did his wife have to indulge in her emotions to the point where she died of grief. Even in situations where the objective reality is beyond our control, our attitude is pretty much the only thing we own---the wealthy and powerful also get sick, old and die. Even random violence affects the wealthy and powerful---many powerful people died in the September 9/11 attacks. The only really wealthy people are ones who wants are less than their resources. The only really secure are those who do not fear death.
Once Ch'iu gets that little glimpse of satori, things change.
Ch'iu Ch'ang-ch'un looked around him and saw everything in a new light. The forest was dancing in the sunlight, and the air was pure and fragrant. It was as if a fog had lifted and an unlimited view was now laid out before him. (p 140)He is not a totally realized man by this point. But this experience is a taste of what it can be like to embrace the void within and merge with the Dao without. These sorts of experiences are valuable in that they give you strength to carry on, but they can dull with time and become forgotten.
Another character, Sun Pu-erh, goes through a stage where she becomes "stuck" in her practice. Paradoxically, this occurrs because she is so intelligent that she quickly masters an introductory practice and assumes that this is all she has to learn. She only gets over this folly through the help of her husband, Ma Yu, whom she finds initially surpassing her in attainment. He points out that it is because he is so much less intelligent than her, that he has simply assumed that he has much more to learn, so he kept seeking out more knowldge after he has gained a level similar to the one she is at.
Ch'iu Ch'ang-ch'un understands the problem of backsliding and the stalled practice, however, so he designs a practice to totally rid himself of delusions. Whenever he notices a delusion intruding into his consciousness, he rolls a large bolder up a nearby hill and rolls it back down into the valley below. This practice---so similar to the myth of Sisyphus---is specifically difficult and pointless, as such it is perfect for training the mind. As such, it serves as a pretty good metaphor for just about every active form of meditation practice I can think of---such as chanting, reptitive ritual kowtowing, etc.
One point that the book also points out, however, is that each individual has to find a practice that works for him. Ch'iu rolls is stone up and down the hill. In contrast, however, Liu Ch'ang-sheng, finds himself suffering from lust. The way he gets around this problem is not by trying to force these thoughts out of his mind, however, but rather by investigating and learning all he can about it.
He gets this insight from an anecdote that is related to him by another Daoist. It seems that a master tested his students to see if they could control their lusts and only one student passed. When the master asks him why he passed whereas everyone else failed, the student says that before he became a Daoist he was someone who used to spend all his free time in brothels and eventually damaged his health by chasing sing-song girls. Eventually, he came to the point where he was totally disgusted by the situation he found himself in (or, as Alcoholics Anonymous would say, "he hit bottom"). Liu doesn't go to the brothel in order to have sex until he too "hits bottom", but the practice of being around prostitutes all the time takes away all illusions and pretentions. He would eventually hear what prositutes really think about their clients, no doubt he would also see ones die from botched abortions, see the poorer ones sell their children into slavery, and so on. This sort of thing eventually weans most people of any obsessive interest in sex---which was the whole point.