What makes it so hard to believe?

One of the ironies of the validation trap (and what makes it a trap essentially) is that the hungrier one is for validation, the more starved one feels for it (and vice versa). I feel this way recently, despite the fact that by all accounts it has been all around me. Today was more than a perfect example, yet somehow the inadequacy somehow shines through and I feel like an imposter.

This morning I had an interview for a somewhat senior contract job at a major hospital in my city. I have been out of work now for several weeks (months) now and having already turned down at least one job, and having been offered another one earlier in the week, I found myself suited and tied on "casual Friday", and meeting with a likeable Irish recruiter in preparation for my time on the hot seat upstairs with the client. When the time came I found myself sitting through a committee-style interview with the department head, the team lead, and the "mobile" point-man (woman). Nonetheless I felt confident and I really knocked it out of the park, even while feeling like I had flubbed it.
This afternoon I met with a recruiter for another job, and once again I approached it with that confidence which really changes everything, and I managed to put myself out there for a job for which I might not otherwise have the qualifications.
This evening I attended an event at my club, which was sponsored for delegates to the national convention. I went with M., my friend and partner in crime, and as is our custom we made the best of the room. We ended up leaving with some other folks from the national council and stayed out for a bit at a bar around the corner from the club. I was delighted to have met a very interesting woman, C., and enjoyed the opportunity I had to connect with her.
And just when I thought the evening was over, as I drove home from downtown to my apartment in the west end, I bumped into my roommate, and between the two of us we actually managed to solve the problems of the world, in an hour, or two. In fact we shared a great deal more than that and  more than I ever imagined we would.
So why am I still so convinced that something is missing? What makes it so hard for me to believe that this is actually working, that life is good?