dauntless and fearless are synonyms. The difference is that fearless is without any fear at all. Dauntless allows for fear, but with effort the fear can be overcome.
Uncertain: shows a hesitancy about what is to be done. Neither of the two words suggest uncertainty.
Impulsive: action that is not well thought out. Neither of the words suggest that an action is impulsive.
Inflexible does not have to do with fear. It just means that there is no turning back from a course of action that others may more open to alternatives.
