What is a bit ambitious?

Excuse me, could you please elaborate on the phrase "what is a bit ambitious"? It seems to suggest that something is striving for something more than what is typically considered achievable or reasonable. Could you give an example of a situation where someone might describe their goals or aspirations as "a bit ambitious"? Is it meant as a positive or a negative comment, or does it depend on the context? I'm curious to understand the nuances of this expression.