A mentor is an older, more experienced person who gives advice and guidance to a less-experienced person. The word comes from the Greek word meaning "to be with". The age gap between the two parties is not important, it's just that one party would like to learn from another.
Reason 1: Unbiased Feedback
The first reason why you need a mentor at work is that mentors give you unbiased feedback. Mentees can be an internal threat to a mentor, as much as competitors are external threats. This is because a potential mentee could become a manager and compete with the mentor for a promotion. Therefore mentors will want to give their mentees internal feedback, but may not want to give them external feedback because it may end up backfiring on them.
Reason 2: Support and Protection
The second reason why you need a mentor at work is that mentors will support and protect you. When someone has your back, you will be more likely to stand up to your boss, or go "above his head" if necessary. With a good mentor, he or she is your "first line of defense" in your career.
Mentors will keep an eye on your career, and if they notice any conflict between you and your boss then they will help resolve the problem. For example, if you tell your boss that he is always criticizing you and that he should treat his employees better then the mentee may be able to go above his head and get a meeting with him.
The day may come where your next step up the career could put you in a position face-to-face with your mentor as an interviewer. Knowing how senior people in the company thinks early on at work can help you acclimatise and "get used to the place" more quickly and if you get hold of a mentor who's basic and straightforward, then you'll be unafraid of asking questions anytime anywhere. The best way to ask is where no one judges!
Reason 3: Information and Connection
The third reason why you need a mentor at work is that mentors can provide information and connections. Not only does this help your career, but it also helps everyone involved. For example, if the mentor has friendships with other managers then this can lead to open doors for you which may otherwise have been closed. Also, a mentor may know about a job opening somewhere else in the company that he or she can tell you about.
Reason 4: They Keep an Eye On You
The fourth reason why you need a mentor at work is that mentors will remind you of what is important to your career. There is a tendency for people to get sidetracked and lose sight of their career goals. A mentor can bring someone back on track if this happens. He or she knows the business and what the priorities are so they can help you stay focused on your career path.
Reason 5: They Analyze You As a Friendly Third-Party
The fifth, final and most important reason why you need a mentor at work is that mentors can tell you about your strengths, weaknesses and opportunities for improvement. A good mentor will be able to help you in any way they can, including developing your skills in areas where you are weak. He is your friend who sees you from your exterior whilst you try your best from the inside out. In other words, a mentor will help you grow and become a better employee.
A final word of advice: Never think of a mentor as a "coach" or "guide". A coach helps an individual get better at a sport or a skill. A guide helps an individual get around a place or to get to where they need to go. Neither of these are what mentors do, mentors either have your best interest in mind, or they don't share the same goals as you.
If you want to get ahead in your career, then follow this advice and find yourself a mentor. It will be the best decision you could make for your career.