ADV
此中;在這里面
You can use herein to refer back to the situation or fact you have just mentioned, when saying it is something such as a problem or reason for something.
例句
The point is that people grew unaccustomed to thinking and acting in a responsible and independent way. Herein lies another big problem.
關鍵是人們已不再習慣以一種負責任的、獨立的方式去思考和行動。這其中就存在另一個大問題。