SB 10.4.38

yathāmayo ’ṅge samupekṣito nṛbhir
 na śakyate rūḍha-padaś cikitsitum
yathendriya-grāma upekṣitas tathā
 ripur mahān baddha-balo na cālyate
Synonyms: 
yathā — as; āmayaḥ — a disease; aṅge — in the body; samupekṣitaḥ — being neglected; nṛbhiḥ — by men; na — not; śakyate — is able; rūḍha-padaḥ — when it is acute; cikitsitum — to be treated; yathā — and as; indriya-grāmaḥ — the senses; upekṣitaḥ — not controlled in the beginning; tathā — similarly; ripuḥ mahān — a great enemy; baddha-balaḥ — if he becomes strong; na — not; cālyate — can be controlled.
Translation: 
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.