Ramayana, Kishkindha Kanda 4.1.121Anushtubh
उत्साहो बलवानार्य नास्त्युत्साहात्परं बलम् । सोत्साहस्य हि लोकेषु न किञ्चिदपि दुर्लभम् ॥
Enthusiasm is the true strength, O noble one! There is no power greater than enthusiasm. For one with enthusiasm, nothing in this world is unattainable.
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