CC Madhya 14.163
ato hetor ahetoś ca
yūnor māna udañcati
“ ‘The progress of loving affairs between a young boy and a young girl is by nature crooked, like the movement of a snake. Because of this, two types of anger arise between a young boy and girl — anger with a cause and anger without a cause.’ ”
This is a quotation from Śrīla Rūpa Gosvāmī’s Ujjvala-nīlamaṇi (Śṛṅgāra-bheda-prakaraṇa 102).