Whilst I do not believe that a feeling of insecurity is a good thing and can have a negative impact on your performance, I think that a feeling of 'lacking current knowledge' is a good thing and drives you on to improve yourself.

If you feel insecure at least some of your focus will be on those insecurities. For instance if you feel your job is not secure you will focus (perhaps) on looking at other jobs.

If you feel that there are folk out there who know more than you or are better DBA's than you then, for me at least, that is the stick for self improvement.

Don't we always want to be the best? Top dog?

I know I do!