CC Madhya 8.201

rādhā-kṛṣṇera līlā ei ati gūḍhatara
dāsya-vātsalyādi-bhāve nā haya gocara
Synonyms: 
rādhā-kṛṣṇera līlā — the pastimes of Rādhā and Kṛṣṇa; ei — this is; ati — very much; gūḍhatara — more confidential; dāsya — of servitude; vātsalya-ādi — and of parental love, etc; bhāve — in the moods; haya — is not; gocara — appreciated.
Translation: 
“The pastimes of Rādhā and Kṛṣṇa are very confidential. They cannot be understood through the mellows of servitude, fraternity or parental affection.