Field of Dreams reference, right? Right!

叩けば埃が出る
(Tatakeba hokori ga deru; “If you strike it, dust will come out.”)

Definition:

No matter how much you smooth over the surface of something and make it presentable, closer inspection will reveal flaws; no matter how polished a person’s surface is, looking closer at their dealings or their past will reveal improprieties. The image is of a surface that looks clean and polished, but which yields dust when struck. By extension, the idea that every human has weaknesses and failings; we’re all only human. Note that this saying only talks about negative features; it can’t be used in reference to hidden talents or good points.

Breakdown:

We begin with the verb 叩く (tataku) in its subjunctive form, followed by a verb phrase comprising a noun – 埃 (hokori), “dust,” and a verb – 出る (deru), “to come out,” in sentence-final form. Although this noun is attached to the subject-marker particle が (ga), it is only the grammatical “subject” of the verb phrase; the sentence as a whole has an indeterminate human actor as its unspoken subject. In English we express this subject as the indeterminate “you” or, if you’re feeling fancy, as “one.”

Notes:

This saying has a number of synonyms, including a version in which the final verb is replaced with 立つ (tatsu), “to rise.”

Example sentence:

「どんな政治家でも叩けば埃が出るというが、彼奴は取り繕った表面すら欠けている。ただの埃の塊が行動していると言ったら良いかな」

(“Donna seijika de mo tatakeba hokori ga deru to iu ga, aitsu wa toritsukurotta hyoumen sura kaketeiru. Tada no hokori no katamari ga koudou shiteiru to ittara ii ka na.”)

[“They say any politician will have drawbacks if you look close enough, but that guy lacks even a polished surface image – you could say he’s just a walking pile of drawbacks.”]