bô-sū-bô-pe̍k無事無白

without cause or reason

without cause or reason; for no reason at all

English Wiktionary, “無事無白” (CC BY-SA 4.0) — https://en.wiktionary.org/wiki/%E7%84%A1%E4%BA%8B%E7%84%A1%E7%99%BD · confidence: Medium (Wiktionary)