It's the same as doubting one own self. It's a poison that disintegrates own confidences and breaks up one's hope for better future.
Lately been going through hard times with a difficult boss who never appreciate your hard work and only sees your bad points, so much so that I began to doubt my own self as well... My eyes have been swollen for couples days.
Now that I have decided to move on, I felt so much better and I'm looking forward to better life ahead.
I too wish every one out there not having to go through such dark periods. Never Self Doubt.