初生之犊不畏虎

chū shēng zhī dú bù wèi hǔ

lit. a new-born calf has no fear of the tiger (idiom)

fig. the fearlessness of youth

chū

at first

shēng

to be born

zhī

(possessive particle, literary equivalent of 的[de5])

calf

no; not so

wèi

to fear

tiger