The subtlety of the Buddha-dharma is described by Chih-i as follows:

“The hundred realms and the thousand suchnesses are the objective realm of the Buddha, and only Buddhas … can exhaust such principle [reality]. It is like a huge box: its cover has to be correspondingly huge too. With the unlimited Buddha-knowledge, [the Buddha] illuminates the vast and great Buddhahood and objective realm. For [the Buddha] to reach to the bottom [of this reality] is called ‘following his own will.’ If [the Buddha] illuminates the characteristics of the nine other Dharma realms from beginning to end without leaving out a thread or a mustard seed, this is called ‘following another’s will.’ On the basis of these two dharmas [of following the Buddha’s own will and another’s will], [the Buddha] manifests the Traces of the ten realms, either showing his own body or another’s body, and either speaking the words following his own will or the words following another’s will. Both his own will and another’s will are inconceivable, and both his own body and the body of another are extremely subtle and quiescent. [Ultimately,] all of them are neither Relative nor Ultimate, and yet, [they] are capable of responding to the Relative of the nine realms and the Ultimate of the one realm, causing no loss or decrease to the Buddha-dharma.” (Vol 2, Page 81)