It is the emotion that questions the course you have chosen, or the goal you have set.
It is a cautionary emotion, that if not seriously addressed, might seriously derail the decision-making process. The doubt energy could be about the goal you have, it could be about how you are spending your energy and time. Once it gains in vigor, the manager/leader needs to take the time to examine how this emotion is influencing the decisions or communication patterns and actively inhibiting productivity.
If “doubt” gains ground, internally in the self or the team, the project itself maybe disbanded.