Yuanyun Jiexian was a master of the Linji lineage, who lived from 1610 to 1672. This is an excerpt from his writings of advice for Chan masters teaching students using the huatou method. In this case, the huatou is the focus point of a broader koan. For example, "The myriad things return to one. What does one return to?" or "What was your original face before your parents were born?"
In this excerpt, he's advising Chan masters in directing the specific needs of different students during a seven-day meditation retreat, and the importance of the master in having interviewed every single student and know precisely where they're at and which huatou they are working on.
He then lists the various ways that students working on a huatou can go astray.
...
When the master goes to the Chan Hall, he must first know the names and faces of everyone in the congregation and the huatou that each one of them has made his basic investigation. Only then can he set to work to train and temper them. If the master does not know the people he is dealing with, then even if they gather together for ninety days, they will be like passing strangers.
If the master knows the people but does not know their fundamental question, then when the Chan master comes down to the Chan Hall and wants to engage the practitioners and press them to advance, he will have no way to do so.
If a Chan master wants to know these things, the method is to have practitioners enter his private room and to probe and test them and cut away their illusions. In general, people vary in their basic capacities, and there are many different kinds of investigation and learning.
Some may understand huatous intellectually but lack the will to come to grips with them and investigate them.
Some cannot develop a decisive will in their investigation or are hesitant to go all out.
Some have the will but cannot generate the doubt sensation.
Some get caught up in wandering thoughts as soon as the huatou is brought forth.
Some investigate for years without knowing how to do genuine meditation work, and so accomplish nothing.
Some draw theoretical principles from the scriptures and seek to align these to the huatou.
Some just make use of the huatou to dispel wandering thoughts.
Some hide away inside the armour of "non-doing" and lay to rest their sense faculties.
Some stubbornly follow their subjectivity and take it as their own master.
Some recognise seamless silent annihilation as complete realisation.
If there is no genuine Chan master to set the people who fall into these errors straight, and they have no real inner doubts, all sorts of sicknesses will develop. In all of these cases, when the practitioners who harbour these illusions enter the master's room, the master must search out and expose these illusions one by one and utterly sweep away each and every one of them.
The master must dissolve the sticking points and remove the bonds for the practitioner, banish his fixations and wipe away his confusion.
The master cuts the entanglements that the practitioner brings along with him and cures the mortal illness that has entered deep within him.
If the master directs the practitioner towards genuine investigation, then the road he follows is sure to be correct.