Several parts combine into one character.

In oracle bone script, 事 shows a hand (又) gripping the shaft of an official banner — the hand of a clerk on duty at the ancient yamen, doing the day's administrative work. The original sense was "to attend to official business," and from that root the meaning expanded outward to "matter, affair, incident, to serve." 事 and 仕 share the same ancestral branch — both are about the work of officialdom — but they split early.

Korean reading "sa." Genuinely high-frequency in Sino-Korean vocabulary: 事業 (saeop, business / undertaking), 事故 (sago, accident), 事件 (sageon, incident), 人事 (insa, personnel / greetings), 萬事 (mansa, all things), 無事 (musa, safe). It covers nearly every Korean word for "matter."

Mandarin shì, 4th tone. Top-frequency in spoken Chinese: 事情 (shìqing, matter / affair), 事故 (shìgù, accident), 事业 (shìyè, career), and the conversational gem 没事 (méishì, "no problem / it's fine"). 没事 is one of the most reflexive phrases in casual Mandarin.

Japanese on-reading ジ powers 仕事 (shigoto, work — note the 仕+事 doubling), 人事 (jinji, personnel), 無事 (buji, safe and sound). But the real story is the kun-reading こと (koto): 事 alone, read as koto, is the most common abstract noun in Japanese — "thing, matter, fact, situation." Phrases like ことがある (koto ga aru, "there is the case of...") build the grammar of everyday Japanese.

Memory aid: a hand holding a banner — the official on duty, attending to matters.