People who arouse a true and genuine aspiration and engross themselves in study to the full extent of their capacity, do not fail to attain. As for the description of the essential point to be mindful of, what thing must be concentrated upon, what practice is to be considered most urgent, that is as follows.
First is only that the aspiration of joyful longing be earnest. …while travelling, abiding, sitting and reclining, in the midst of affairs as the pass, though various different events come up, he goes along seeking an opening, his mind occupied [with his quest]. With his mind so forcefully earnest, there can be no failure of attainment.
In this way, when the aspiration to seek the Way has become sincere, either during the period of sole concentration on sitting, or when dealing with illustrative example of the people of olden times, or when meeting the teacher, when one acts with true aspiration…
Unless you arouse a mind comparable to this, how will you accomplish the great task of the Buddha-Way, which cuts of the turning round of birth and death in a single instant of thought?
If someone has such a mind … he will definitely attain enlightenment.
~Eihei Dogen, Record of Things Heard (zuimonki), II:15, Thomas Cleary