I am blessed to work with people from a broad range of organizations and levels of responsibility within those organizations. Here's what I've found. People don't give themselves credit for what they know and do. When you do something naturally and for years on end, you begin to believe that anyone could do it as well as you do. Your expertise is transparent to you and you forget that you really are an expert - that a small percentage of the human population is able to provide what you provide.
You're an expert - now act like it!
What does it mean to act as an expert? It means you have four characteristics.
Characteristic #1: You are self-aware
You know what you know and, hopefully, you know what you don't know. You don't think you know everything, but you realize there are some areas of life you understand very well - far better than the average person. Whether it is how to write a mortgage, open an investment account, teach 2nd graders, or comfort a family when a loved one dies, you know you are skilled at what you do.
Characteristic #2: You are confident
Arrogance is misplaced confidence. Confidence is acting from security and without worrying about how everyone else will react. You know what you are doing and you don't have to have every action approved by someone else.
Characteristic #3: You are a lifelong learner
You keep learning and growing. You are better today at what you do than you were five years ago and better than you were 12 months ago. Your trajectory is up.
Characteristic #4: You are a specialist
Within your area of expertise you may act as a generalist, but compared to the general public you are a specialist. Despite my expertise in anti-slavery rhetoric of the 1820s and 30s, I ended up at a college where I taught Mass Media and Interpersonal Communication in addition to History of American Public Address. Within my field I acted as a generalist but compared to most I am a specialist in human communication.
Quit acting like an unexposed fraud - act like the expert that you are! Act with self-awareness, confidence, continuing growth, and expertise.