It's the vocabulary, it's the complexity of the thought, and so on that makes it difficult. Iser acknowledges this.

是词汇，思想的复杂性等等,使它变得难懂，伊瑟尔承认这一点。

耶鲁公开课 - 文学理论导论课程节选

It's probably among the most useful ideas there is for solving complicated problems.

这大概是解决复杂问题,最有用的思想之一。

麻省理工公开课 - 计算机科学及编程导论课程节选

That won't allow us to communicate complicated ideas.

我们无法用这些词来进行复杂的思想交流

耶鲁公开课 - 心理学导论课程节选