志 (zhì): Aspiration, ambition, will, goal. It represents a person's inner drive and highest aims.
大 (dà): Big, great, grand, large. Here it emphasizes the scale of the ambition.
才 (cái): Talent, ability, skill, competence. This refers to one's actual, demonstrable capabilities.
疏 (shū): Sparse, scarce, scanty, thin. It can also mean negligent or careless. Here it means that the talent is thin on the ground.
How they combine: The structure is a perfect parallel: “Ambition (is) Great, Talent (is) Scarce.” The juxtaposition of 大 (dà) and 疏 (shū) creates a powerful contrast that immediately conveys the core meaning of imbalance and inadequacy.