There is a fine line between proper and realistic self-confidence and reckless self-confidence. The latter (recklessness) often appears in the religious as a belief that the Lord will not let anything bad happen to you - that you can do anything without concern for the potential consequences - that you deserve to have good things happen to you and that nothing is an un-necessary risk.
There is realistically being aware of one's strengths and weaknesses, and there is being aware of one's strengths and blind to one's weaknesses - and there is being aware of one's strengths and blind to others' weaknesses (which is a weakness, in and of itself). I do not advocate blind and/or all-encompassing confidence. Even Ammon, who was one of the greatest missionaries in our recorded canon, gloried "in the Lord" - and humans have a tendency to think the Lord will help them get whatever THEY want, rather than what HE wants to accomplish through them.