A noun which means a flaw in achieving something
Solution 1:
Without more context its hard to say. "His flaws hinder him" works in a general sense, but if you want to be more specific, context is needed.
But speaking specifically to the 'lacking' aspect - perhaps deficiencies is a possible answer:
From Merriam-Webster:
: the quality or state of being defective or of lacking some necessary quality or element : the quality or state of being deficient : INADEQUACY