盲蛇に怖じず
(Mekura hebi ni ojizu; “The blind do not fear snakes”)

Definition:

The ignorant have no way to judge the true danger of a situation, and so take risks that more knowledgeable people would avoid. “Fools rush in where angels fear to tread.”

Breakdown:

We begin with the noun 盲 (mekura), “blind (person).” This is followed, with particles elided, by the noun 蛇 (hebi), “snake.” And at the end we have the verb 怖づ (odzu), “to be afraid,” in imperfective form (although note the orthographic shift from ぢ to じ in expressing the pronunciation ji), followed by negative suffix ず (zu) in sentence-final form. In between the final noun and the verb, directional particle に (ni) marks the snake as the thing not being feared.

Notes:

This saying can be referenced with just 盲蛇 (mekurahebi), but be careful – this is also the name of the Brahminy blind snake.

Example sentence:

「無理に挑戦するとひどい目に合うぞ、とどんなに警戒されても、やっぱりやってみたい。盲蛇に怖じずという状況かな」

(“Muri ni chousen suru to hidoi me ni au zo, to donna ni keikai sarete mo, yappai yatte mitai. Mekura hebi ni ojizu to iu joukyou ka na.”)

[“They all warn me that it’s too hard, and going for it will only get me in trouble. But no matter how much they say it, I still want to try. Perhaps I’m like the blind man unafraid of the serpent.”]