The dilemma, of course, for the mentor involves the difficult task of remaining a positive advocate for the mentee while also fulfilling the mandate of offering the best possible advice based on careful observations, sufficient information, and honest conclusions.
One pragmatic solution to the problem is to allow mentees the opportunity to test their own plans in the world so that they can obtain the necessary personal and professional reference points that are often a prerequisite for meaningful self-realization.
This is an especially valuable learning pathway, especially if the mistakes are not particularly costly, the mentees will recover from the experience with their egos sufficiently intact, and the probability is high that they will regain their balance and continue on their journey, perhaps with modified maps.