When I was very small, I had the ambition to be either a scientist, a private investigator or an army dude.
Later, in my teens, I wanted to be Super Soros Level 4 - the ultimate currency speculator.
What I learned from all this bullshit is that being ambitious is only cute when you're below 18 years old. Over that age, ambition can kill you. Water that floats a ship can also sink it, said Wong Fei Hong's father - Wong Kei Ying - in Drunken Master 2.
On a basic level, ambition is basically creating a scene in the future. A vision of success, victory, justified celebration, etc.
The problem with this is that it diminishes your connection to the present. If you constantly live in the future, there is no time for the present.
Also, you begin to see the present as a means to an end. In that, there is resentment and resistance to the present. This creates unhappiness, and what kind of future can you create, with pain and suffering?
Over the years, I have seen many friends - good people - get consumed by the fires of ambition, by the fires of desire. For ambition is nothing but desire, and all pain and suffering comes from desire. What power would hell have, if the denizens cannot dream of heaven?
All suffering ever is, is non-alignment with the present. With ties either to the past or the future. Basically, pain is a case of time warped mental situations.
So go forth and have your ambitions, but be careful. Water that floats a ship can also sink it.