If someone showcases great insight, which of the following words best describes them?

The term that best describes someone who showcases great insight is "acumen." This word refers to the ability to make good judgments and quick decisions, particularly in a specific domain like business or a particular aspect of life. When a person has acumen, they demonstrate a sharpness of mind and a keen insight into complex situations, which aligns perfectly with the idea of showcasing great insight.

In contrast, the other options—such as "diffident," which describes someone who is shy or lacking in self-confidence; "acerbic," which refers to a sharp, biting, or sarcastic tone; and "ascetic," which describes a person who practices severe self-discipline and abstains from indulgence—do not capture the essence of having deep or profound insight. Thus, "acumen" is the most suitable choice as it pertains directly to insight and keen understanding.