SB 10.4.38
yathamayo ’nge samupeksito nrbhir
na sakyate rudha-padas cikitsitum
yathendriya-grama upeksitas tatha
ripur mahan baddha-balo na calyate
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As a disease, if initially neglected, becomes acute and impossible to cure, or as the senses, if not controlled at first, are impossible to control later, an enemy, if neglected in the beginning, later becomes insurmountable.