English to French Social Sciences Human Resources Talent assessment

A key feature of the motivation of highly successful people is that they are driven to make a distinct impact on the world. People with potential have an attitude that is to question and challenge how things happen. Their concern is to leave a personal legacy by setting themselves goals which focus on the achievement of broad impact. People with such drive are essentially confident and assured of their abilities. However, ***underlying this is a degree of insecurity*** that can be surprising for other people. Insecurity fuels their concern to make a difference. They show a high level of initiative. They are prepared to step back and question other people and their environment. They need little close direction, preferring to operate with some autonomy in setting objectives.

Mon problème n'est pas de traduire. J'ai beau relire le paragraphe, je ne comprends pas ce que "insecurity" vient faire au milieu de toutes les qualités énoncées.
Est-ce que cela veut dire que les personnes trop sûres d'elles manquent en réalité de confiance en elles-mêmes??