Unattainable (adjective)

1. Not able to be reached or achieved.
2. Not able to be obtained or achieved.

Origin:

From un- + attainable, first recorded in the late 16th century.

Examples:

1. The goal seemed unattainable at the time.
2. The summit was unattainable due to the bad weather.
3. The dream was unattainable without a lot of hard work.
4. The objective was unattainable without the necessary resources.
5. The prize was unattainable for lack of skill.