Often implies inconvenience or a negative outcome that was not planned for. Their picnic was ruined by an unforeseen storm.
Pro Tip 2/3
Not Always Bad
Can also refer to positive surprises, like a beneficial event or opportunity. The unforeseen success of her book led to a series of interviews.
Pro Tip 3/3
Neutral Contexts
Used in business or planning contexts to describe events that could not have been predicted. We need to allocate funds for unforeseen expenses in the project.