Unrealistic (adjective)

1. Not having a basis in reality or fact.
2. Not achievable or appropriate to the circumstances.
3. Exaggerated or foolishly optimistic.

Origin:

Mid 19th century: from un-1 (expressing negation) + realistic.

Examples:

1. Her expectations of a perfect marriage were unrealistic.
2. The deadline was unrealistic given the amount of work that needed to be done.
3. The plan to solve all the world's problems in a single day was unrealistic.
4. Her belief that she could win the race without training was unrealistic.
5. The company's revenue projections were considered unrealistic by industry analysts.