expression, ichidan verb
to have one's faults exposed; to have one's secrets blown
Idiomatic expression meaning that hidden flaws, secrets, or incompetence become apparent, often unintentionally. The image is of rags or tatters showing through a disguise.
彼は普段は冷静だが、トラブルが起きるとすぐにボロが出る。
He usually seems calm, but when trouble arises his faults quickly show.
嘘を
Even if you lie, your secrets will eventually come out.