I would like to help you with your question.
I can understand the frustration from never seeming to be satisfied with your own accomplishments. Sometimes these feelings arise from the expectations others have set for us and our belief that we have to live up to those expectations. Insecurity and low self-worth might also be at play.
It would be helpful if you would give me a little more information. How long has this been going on? Do you know what this great thing or great somebody that you have been chasing? Do you think you have been at all successful in life?
Do you feel that others expect more from you than you can reasonable attain?
I await your reply.