This concept is so tired! If you grind for years to mastery under the tutelage of true masters, you feel no imposter syndrome - you feel confident and complete in yourself. Temet Nosce
I am usually fairly confident. But then I will come across something where I realize I have missed a whole field in what I do. That is when it kicks in for me. Then I realize oh wait I can do this just need to put some time into it. Just like the previous five thousand times...