That's right - Lack of Self Esteem. Which is of course directly linked to lack of self-efficacy, which is related to subscribing to the wrong set of beliefs. Beliefs like taking "Don't work hard, work smart" to the extreme. Like "Don't worry, you are unique - just like everyone else." And like "The customer is always right."
No doubt about it, we all need to work hard and smart to grow and improve ourselves every day. One percent per day is a good start. Twice as good in seventy days. If you don't want to work that out, just use a spreadsheet and see for yourself.
Get up. Go out, meet people, form mutually beneficial relationships. Forget about "work-life balance", there is no such thing! It is called "Work-life harmonization" or "Work-life Integration." Ignore people who keep telling you to "simplify" your speech, your emails, your messages, when what you really hear is "dumb down your language." Become good at language. It gives you a wide repertoire of subtleties, nuances, shades of meaning, and allows you to become much more descriptive than you are right now. That makes for better stories, and people do like stories, don't they?
In order for you to become better, work on something! Get yourself trained in what you need. Determine your own attitude each day and each time you meet someone who could become a client or customer. You do not know all the answers, that is for sure, but what is stopping you from becoming conversant with topics in and around your spheres of control, influence and interest more and more each day? Your brain's not going to choke on too much data. After all, you're not expecting to be living in this body for three million years, are you?
Stop whining about how good you are, but nobody's noticing you. Develop yourself in areas you need to, start becoming interested in other people, and think about how you can help others. That's your one percent for today.
P.S. By the way, do you realize that if you flip that "improve by one percent per day, in seventy days you're twice as good" truism, what you get is that if you don't improve by one percent per day, your effectiveness, quality of life, etc, get half as good in seventy days? I don't have research to prove it, but I'll bet it moves in that direction. Now, I know we don't lose acquired skills like riding a bike, but you know what I mean. Make no mistake, effort is still required when you're on cruise control. Entropy is universal and it takes constant effort to reduce deterioration.