As people gain success in their life they tend to lose track of what is really important because their ambition blinds them from the consequences of their goal. For example wanting to gain a better position at work could cause a person to spend more time there than at home and strain their personal relationships. In the end the person could be higher on the workplace ladder but unhappy in their life with the people they care about.
Ambition is also a personality trait that is never satisfied with what it has. People who are extremely ambitious tend to have multiple goals, and when reaching one start on another. This is good because it is ambitious people who progress society in all aspects of life. But we should also sometimes be content with what we have and recognize when to stop and enjoy it.
I think people should have ambition because it is what motivates us to do things that help advance ourselves and sometimes society. I think that it helps people aspire to do great things for themselves and others and is what progresses civilizations into better ages. But I also think that ambition without thinking of consequences can sometimes be more harmful then beneficial.