The expert represents a person with imposter phenomenon that never feels good enough despite valid qualifications. This person may feel like they are less experienced than their colleagues if they do not know an answer or have knowledge on certain topics.
general tips
It's true that there's always more to learn. Going beyond what's expected of you at work can help you excel professionally and get noticed in a competitive job market. Taken too far, the tendency to endlessly seek out more information can actually be a form of procrastination.
Start practicing just-in-time learning. This means acquiring a skill when you need it–for example, if your responsibilities change–rather than hoarding knowledge for (false) comfort.
Realize there's no shame in asking for help when you need it. If you don't know how to do something, ask a coworker. If you can't figure out how to solve a problem, seek advice from a supervisor, or even a career coach. Mentoring junior colleagues or volunteering can be a great way to discover your inner expert. When you share what you know, it not only benefits others, but also helps you redirect your fraudulent feelings.
"Every time I was called on in class, I was sure that I was about to embarrass myself. Every time I took a test, I was sure that it had gone badly. And every time I didn't embarrass myself — or even excelled — I believed that I had fooled everyone yet again. One day soon, the jig would be up..."
— Sheryl Sandberg, Chief Operating Officer of Facebook