Kural - 474

Who not agrees with those around, no moderation knows,
In self-applause indulging, swift to ruin goes

Explanation
59 He will quickly perish who, ignorant of his own resources flatters himself of his greatness, and does.

Tamil Transliteration
Amaindhaang Kozhukaan Alavariyaan Thannai
Viyandhaan Viraindhu Ketum.