Monkey versus Horse
In Chinese thought the mind is viewed as having two parts - the emotional mind and the wisdom mind. The emotional mind is likened to a monkey, the Mind Monkey. A monkey that chatters constantly and jumps around from branch to branch (or thought to thought). It is powerful and very hard to train. It is the Mind Monkey that gives us the many excuses why we don't need to do what's good for us - keep to a nutritious diet, exercise regularly, rest adequately, working on our Gongfu consistently. It steers us from the disciplined path to the easier, possibly lazier path.
The wisdom mind is likened to a horse, the Thought Horse. A horse that is quiet and consistent. It can be set a task and can work on that task to completion. It is powerful and somewhat easier to train. It is the horse that helps us make wise choices and to be disciplined for the long term. The trick is caging the monkey long enough to work with the horse to achieve worthwhile results. This gets easier the more we practice it. We can also use our breath in ways to enhance the power of the horse and subdue the power of the monkey.
If we can achieve regular use of the horse mind then there is unlimited potential to achieve anything we want. Consistency and regularity is the key.
We say that the miind is a 'mind monkey' or 'thought horse' because like monkeys and wild horses, the mind is very difficult to tame and control. Enlightenment is not possible in a state of a scattered mind.
Only when you collect your attention again and again from wandering and achieve a peaceful and focused state will you have a chance of attaining enlightenment.
This is taming the 'mind monkey' and reining in the 'thought horse'.
From Attaining the Way by Zen Master Sheng Yen,
Shambala Publications, 2006