Mentors: Aristotle's model
The best mentors are often those who have wide knowledge: they are not overly specialized in one field; they can train you to think on a higher level, and to make connections between different forms of knowledge.
The philosopher Aristotle is the ideal model for a mentor. He had learned and mastered so many different fields, he could teach Alexander the Great an overall love for learning, teach him how to think and reason in any kind of situation.
But it is not always possible to find a perfect mentor like Aristotle. An alternative strategy is to find several mentors in your immediate environment, each one filling strategic gaps in your knowledge and experience.
Maintain some distance from the mentor who overly specializes in one field. But move closer to the one who has wide knowledge. You can compensate for the latter's gaps by bringing in other versatile mentors who will fill those gaps.
Understand: Aristotle kind of mentors can give you guidance in any field, and they allow you to choose your path.

