The word "缘故" is formed through the classical Chinese method of combining two synonymous or closely related characters to create a single, reinforced concept. The character "缘" originally implied a causal link, connection, or condition that leads to an outcome, often with a nuance of fate or circumstance. It is paired with "故", which directly means a cause, reason, or original incident. By joining them, the compound "缘故" strengthens and solidifies the abstract idea of a "reason" or "cause", blending the sense of an underlying connection ("缘") with the concrete idea of an antecedent event or motive ("故") to express the full notion of why something is the way it is.