Combined, the characters literally mean: “An event (事) happening (出) has (有) a cause (因).” It's a very direct and logical construction.
`事出有因` reflects a deeply ingrained pragmatic and rationalist strain in Chinese culture. Rather than attributing events to pure chance or divine whim, there is a strong tendency to look for logical, observable causes. This mindset is crucial in everything from business strategy to traditional medicine, where diagnosing the root cause (the `因`) is essential to treating the symptom (the `事`). A common Western comparison is the phrase “everything happens for a reason.” However, there's a key cultural difference. The English phrase often carries a comforting, spiritual, or fatalistic connotation—implying a grand, perhaps unknowable, plan (“It was meant to be”). `事出有因` is far more grounded and analytical. It's less about destiny and more about forensics. It implies that with enough investigation, the reason can be found and understood, which empowers one to solve the problem or learn from the situation. It's the difference between saying “This was part of a divine plan” and “Let's find out what caused the system to crash.”
This idiom is common in both formal and informal contexts. It's not just an old saying; it's an active part of modern vocabulary.