In a culture that deeply values collectivism, harmony (`héxié`), and interpersonal relationships (`guānxi`), being described as 孤僻 (gūpì) is a significant social criticism. Traditional Chinese society emphasizes the importance of the group over the individual. A person who is 孤僻 is seen as rejecting these fundamental social norms.
孤僻 (gūpì) is a strong word and is used to describe a stable, long-term personality trait. It's not for describing someone having a quiet day.
The biggest pitfall for English speakers is equating 孤僻 with “introverted.” Doing so can lead to serious misunderstandings.