There is a mindset paradox where on one hand you are full and on the other hand you are still hungry. Ambition is not synonymous with contentment, in fact they are on different teams, are we supposed to choose a team?
Thinking about it in this one or the other way, you can see the shadow sides of both. Ambition can be corrupted by greed envy etc, while contentment can lead to laziness detachment etc. There is a balance.
On our boat of purpose, we will need both eagerness and gratitude (among other things like focus, bravery, intestinal fortitude, etc) to navigate the murky waters and find the most flowingest of flows.