Valmiki Ramayana Kishkindha Kanda Sarga 2 Shloka 17
Original Shlokaअहो शाखामृगत्वं ते व्यक्तमेव प्लवङ्गम। लघुचित्ततयाऽत्मानं न स्थापयसि यो मतौ4.2.17।।
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अहो Oh, प्लवङ्गम monkey, यः whoever, लघुचित्ततया with low intellect, आत्मानम् oneself, मतौ in mind,न स्थापयसि cannot be steady, ते to you, शाखामृगत्वम् monkeynature, व्यक्तमेव is very clear.
'Oh monkey, whoever is lilylivered cannot be steady. It is evident that your very nature as a monkey makes you restless.