(Ten ni mukatte tsuba wo haku; “To face the heavens and spit”)
To attempt to harm others is to invite misfortune on yourself. What goes around, comes around. If you try to dirty the sky by spitting on it, the blob of spittle is just going to fall back down on your upturned face.
We begin with the noun 天 (ten), “the sky,” “Heaven,” marked by the directional particle に (ni). The first verb being performed skyward is 向かう (mukau), “to face (toward),” here in conjunctive form to allow for further verbs to be added. The second verb is 吐く (haku), “to spit (out),” in sentence-final form. The particle を (wo) marks as the object of the verb the noun 唾 (tsuba), “saliva,” “sputum.”
This saying will often be shortened to 天に唾する (ten ni tsuba suru, “to spit toward heaven”) or 天に唾す (ten ni tsuba su, same). In all cases, 唾 may also be read as tsubaki.
Apparently some people misinterpret the saying as referring to insolent behavior, and it’s easy to see why, but this is considered incorrect.
This saying comes to us from the Sutra of Forty-Two Chapters, a collection of aphorisms traditionally held to be the first Indian sutra translated into Chinese. The original Japanese rendition seems to have used the verb 仰ぐ (aogu, “to look up (at)”), and some versions of the phrase still use 天を仰いで (ten wo aoide, note the particle usage) rather than 天に向かって.
(“Sono ko wa doukyuusei ni jibun no tsumi wo nasuri tsukeyou to shiteiru tochuu de tsukamatte, jibun no batsu ga omoku natta. Ten ni tsuba su koto wo yoku rikai shite, kimi mo jibun no koudou ni motto ki wo tsukete kuretara, sensei wa ureshii nda yo.”)
[“That kid was caught in the middle of trying to pin the blame for their own crimes on one of their classmates, and it made the punishment that much worse. I’d like it if you, too, learned that trying to harm others will harm yourself, and pay a little more attention to your own behavior.”]