Serious scholarly work (and artistic work) demands perseverance and hard work, and ambition is often helpful as well. Ideally you find problems that engage you, and new ones come along as you work out a problem. Your depth of understanding, your sense of the range of what might be doable, develops in time. Your past work is your specific asset. And of course, you know what others have done.
If you not have that enthusiasm and ambition. you may still make significant contributions to scholarship. Professional ethos, choosing the right problem, and sheer doggedness will often lead to a strong career path.
The literature on Richard Nixon points out his perseverance and resilience, his ambition for respect, his constant reforming himself and his legacy. And of course his talents, and his capacity to do himself in.