It might sound counter intuitive, but as I think about it, feelings of unworthiness have alot to do with pride.
When you feel unworthy, you are effectively saying that God is not enough. Jesus Christ upon the cross, the love of God for us, it is not enough.
Instead, you must with your own two hands climb higher and prove yourself better. You disregards all that God says about you, and instead try to find your worth in your own successes.