inconsistency

I regularly hear from successful adults with ADHD - particularly men - that though they experience success at work they worry that they still don't feel successful.  In fact, they feel as if they have others 'fooled' and that some day they may be discovered as a fraud.  A marriage tip reader recently wrote me to ask "what's at the root of this?  I often feel this way but can't pinpoint why..."  As I've talked with adults in counseling about this issue I believe it has to do with the inconsistency of ADHD.