His timidity proved to be costly.

Answer: Option A

Timidity : lack of courage or confidence.
Boldness : willingness to take risks and act innovatively; confidence or courage.
Arrogance : the quality of being arrogant.
Self-assertion : the confident and forceful expression or promotion of oneself, one's views, or one's desires.
Self-confidence : a feeling of trust in one's abilities, qualities, and judgement.

Antonym of Timidity is Boldness