#shawleveryday2019 Day 74
While Imposter Syndrome is not a mental illness or disorder in and of itself, it is often related to Social Anxiety Disorder and is an example of disordered thinking that can a symptom of a variety of other mental illnesses. Wil Wheaton talks about it in his keynote address at the 2016 Mensa gathering.
Even though there is plenty of evidence to the contrary - good job, loving relationships, nice house, great pets, etc. - there is a constant feeling of being a fraud or that somehow you don't deserve success. Your brain is being irrational and it can be very hard to see reality.
I really encourage you to read Wil's post, because he explains it so much better than I can. You can do a search for Imposter Syndrome to start at that section, but the whole thing is worth a read too.