What is enlightenment? And if one knows what enlightenment is, how is it possible for an ordinary person to achieve the enlightenment of the great patriarchs and masters, much less that of the Buddha?
These are legitimate questions for any follower of the Buddhist path, but, at the same time and somewhat paradoxically, they are irrelevant. We can say that they are relevant questions but they put the emphasis of practice on the wrong goal. It is somewhat like someone in Paris who wants to fly to Beijing but gets on a plane to New York.
How do we resolve this seeming paradox? In the Buddha's basic teaching of the Four Noble Truths and the Noble Eightfold Path, one sees a complete prescription for practice but no mention of enlightenment. What one finds is a set of teachings whereby a follower of the Path can bring cessation to the cycles of birth-and-death and, with that, bring cessation to suffering. This is the fundamental teaching of the Buddha: to bring an end to suffering we practice the Path.
At the same time, the Buddha's own enlightenment is presented as a model of emulation for all Buddhists. The result of this is an exquisite irony in which one works diligently to relieve suffering while putting aside thoughts of buddhahood.
The great achievement of Chan Buddhism is that it sweeps away the seeming contradictions by making contemplation of one's own mind the core of practice, while still having as an aim relieving suffering and attaining buddhahood. It is in mind and its workings that one can find the sources and causes of suffering, as well the seeds of buddhahood. Going one large step further, Chan espouses the Mahayana ideal in teaching that the true path of the bodhisattva is not in relieving one's own suffering but that of sentient beings. In this view, enlightenment is a by-product of practice while still holding it as a goal.