Unanticipated (adjective)

1. Not expected or predicted.
2. Not having been prepared for in advance.

Origin:

Early 19th century: from un- (expressing negation) + anticipated, past participle of anticipate.

Examples:

1. The unanticipated consequences of the policy change have caused concern.
2. The unanticipated weather conditions made the trip much more difficult.
3. The unanticipated success of the movie took everyone by surprise.
4. The unanticipated demand for the product caused the company to scramble to keep up.
5. The unanticipated collapse of the bridge caused a major traffic jam.