arduous

This word carries a heavy sense of exhaustion and prolonged struggle. It describes a challenge that wears a person down over time, rather than a sudden or sharp difficulty. It is typically used in formal or literary contexts to emphasize the sheer scale of the effort involved. While difficult describes any hard task, arduous specifically evokes the image of a long, steep climb or a grueling marathon. It implies that the goal is reachable, but only through relentless persistence and physical or mental endurance.