With experience in business a Mentor can bring an outside perspective to your business proposal.
A mentor is not going to write your business plan, or validate your idea; and nor do they necessarily have the magic answers. What they will do however is steer you in the right direction to get the answers you need, and help you identify gaps that need addressing. Your mentor will challenge your thinking and test your theories, while supporting your decision-making.
A mentor will ask you the hard questions that friends and family may not want to.