Qualifying for a leadership position requires you to take into account something greater than ambition alone. For example, qualifying to lead in a manufacturing business might rely on specialist knowledge of the market or consumer opportunity. Although, it could just as easily be influenced through a relationship with the owners of the business and an understanding of the priorities as they see them.
The fact remains that there are many more challengers for leadership positions than qualifiers. It is also true that clear success indicators exist in most cases and knowledge of them can turn a leadership challenger into a qualifier.
Both challenging and qualifying are essential to the success of any would-be leader but, if challenging for leadership is your decision to enter the race, qualification is what will decide the result.