For the study of Seon, there are three requirements: (1) having the great root of faith; (2) having great determination, and (3) having great doubt. If you lack one of these, it is like a broken like on a tripod sacrificial vessel. In the end you will discard it.
[tr. Miller (2017)]

There are three essentials to Sŏn meditation. First of all, you must be rooted in Great Faith and Great Confidence. Secondly, one must have Great Anger -- a strong, inwardly-directed, ardent determination to practice. Thirdly, one must have Great Doubt. If one of these is missing, it is like a tripod vessel with one leg cut off -- in the end, it will be of no use.
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It is well known that Ganhwaseon practitioners must have three things of essential importance: The first is a Foundation of Great Faith (大信根) for the practice which is possible; the second is Great Zealous Determination (大憤志) of practice to attain enlightenment; the third is a Great Feeling of Doubt (大疑情) on the Hwadu. If one of these is lacking, then it is like a tripod pot with a broken foot and is useless.
[Source]