One of the men who contributed to Phil Jackson reaching his milestone former Chicago Bulls star Michael Jordan was inducted into the Basketball Hall of Fame in 2009.
VOA: standard.2009.12.24
In this example onemilestone might be making the decision to travel by plane and making the reservation.
For the freelance writer who wants to be making a living wage by the end of his second year of business, onemilestone could be the first paid contract.