You see the outside of others.
You see the inside of yourself.
I've heard a few people say recently that they have felt like a failure at certain points in their life. Or just a failure.
Perhaps not meeting the expectations of family. Not being able to achieve the sort of dentistry we see others achieving. Maybe not feeling as rich as others seem.
Recently I was hanging out with perhaps my oldest friend. We've literally known each other since we were born. We don't talk all the time. But when we do, it is easy and effortless with no ego.
I said I admired his business success. He's not a dentist. He's normal 
😉. His business is much bigger. He employs many more people than I do. Develops new technology in his field. Is much more frugal and modest.
Turns out, he envies my business since it seems so high margin compared to his. Selling knowledge seems easier than selling things made of steel.
Since we are close, we can both talk about times that were difficult. However, we can only admit this to our nearest and dearest friends.
So we keep our positive face on for the rest of the world. The one you all see. But behind it, we know our struggles. And those struggles often make us feel like a failure. Sometimes I get a moment where I think I'm a hopeless educator. Or a hopeless businessman. Or a hopeless dentist.
I was feeling this recently. Then I realised, that very few people would look at my posts, or see my dentistry, or my teaching career and be able to believe that I have doubts too. They would never look at the times when finances were tight. Or the time my cases failed, and the patient complained to regulators. Or the time I got poor reviews for a lecture.
You never bat 100%
It's irrational, and it often drives us to try harder and harder and harder. And no matter how much you achieve, that feeling might never go away.
I don't have a solution for you.
Just know that it's entirely normal to feel like you aren't good enough from time to time. Not a good enough parent. Or professional. Or son. Or teacher. Or student.
No matter how good you actually are. 
🙂
