General Motor CEO Mary Barra's career hasn't been shaped by just one or two mentors; instead, it's been influenced network of them.

"Different people see different aspects of us as we progress in our careers and handle the opportunities and challenges along the way," she writes.

Early on, one mentor encouraged her to be more vocal in meetings; another crystallized the importance of honoring commitments, whether they are personal or professional.

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At pivotal moments at work – such as when she had to decide whether or not to take a human resources position at GM, despite her background in engineering – Barra was able to turn to her network, and weigh multiple opinions from people she respected. She writes:

"When building your network of mentors, be honest about your mid- and long-term career goals, and how hard you are willing to work to achieve them. Then turn to those who best know you and your work. Earn their respect and trust so they will extend their personal capital to you with confidence and be your professional champion.

All good leaders should be invested in the career growth of their team members, but don’t always look high when creating your mentor network. Colleagues have great insights about you that you may have overlooked."