Just one detail turning out to be not as expected or not perfect is often enough to shatter their illusions and cause arguing.

illusions 是名词 illusion 的复数形式。illusion 来自拉丁语 illudere（嘲弄、欺骗），指"幻觉、错觉、不切实际的想法"。在这里特指"对事物过于理想化的错误认知"，即"幻想"。 shatter their illusions 这个短语中，shatter 意为"粉碎"，整个短语字面意思是"粉碎他们的幻想"，引申为"打破不切实际的期望"。