Experience

If competence is a combination of knowledge, skills and experience, then the opposite - incompetence – means being inexperienced, unskilled, and/or uninformed. 

Looking at competence from the opposite side provides an alternative perspective. 

If the knowledge is needed, there are books or courses or Google rabbit-holes to explore.  If skills are needed, repetitive action on a task will develop that.  But the one of most interest, and deep down for humans, what is truly looked for when looking for competence, is experience. Experience is crucial for demonstrable competence.  The nominated experience need not be exactly the same but must be relatable.