महाभारत - सभा - शत्रुपक्षं समृद्यंतं

शत्रुपक्षं समृद्यंतं यो मोहात् समुपेक्षते |
व्याधिराप्यायित इव तस्य मूलं छिनत्ति सः ||

- महाभारत, सभा

One must not ignore the ascendancy of a rival. People are usually in denial when they hear about their rivals making good progress. If he does ignore, his enemies will finish him - much the same way as a long ignored disease would finish him.

- Mahabharata, Sabha