A mentor offers more than specific advice, they offer a living demonstration that the difficult path a mentee is currently walking has, in fact, been successfully walked before by someone else, which is often a more powerful source of hope than any amount of encouraging words alone could provide.
This modelling effect works partly because a mentor's example is concrete and specific rather than abstract: a mentee can see exactly what an achievable, realistic outcome actually looks like, rather than having to imagine one entirely from scratch without any real reference point to draw on.
Good mentorship also supplies pathways, practical next steps, connections, ways around a specific obstacle, which combines with the hope the relationship inspires to produce something closer to genuine capability than encouragement alone could ever manage, however well-intentioned that encouragement happened to be. The value is cumulative, built from repetition rather than from any single decisive act.