He would have been successful, but for his lack of temerity.

Answer: Option A

Audacity : a willingness to take bold risks.
Sincerity : the absence of pretence, deceit, or hypocrisy.
Confidence : the feeling or belief that one can have faith in or rely on someone or something.
Strength : the quality or state of being physically strong.
Temerity : excessive confidence or boldness; audacity.

Synonym of Temerity is Audacity