What do you mean?
There are sentences easy to understand that contain a lot of difficult words. On the other hand, there are sentences difficult to understand that contain no difficult words. Generally speaking, it appears that difficult words are difficult to understand and easy words are easy to understand. What makes easy words difficult and what makes difficult words easy when it comes to composing sentences?
There seems to be, in main, three reasons why.
Firstly, when those who write sentences difficult to understand themselves, in fact, don't understand the easy words that they use in their sentences, it becomes difficult for the others to understand the written sentences.
Secondly, when an author composes a sentence merely for the sake of him- or herself, it tends to be difficult for the readers to understand.
Thirdly, where there is no logic, there is no way to understand a sentence even if there are no difficult words in it.
難しい言葉が使われているのに、理解しやすい文章がある。その一方で、難しい言葉が使われていないのに、理解に苦しむ文章がある。普通に考えれば、難しい言葉が使われていれば難しく、簡単な言葉が使われていれば簡単だと思える。
なぜ、作文するという時になると、簡単な言葉が難しくなり、難しい言葉が簡単になるのだろう?
主に3つことが考えられる。
1つ目。簡単な言葉であっても、それを使う人が、実際のところ、その言葉の意味を理解していない場合、他人にとっては理解しがたい。
2つ目。著者が自分自身のためにだけ書いているとき、その読み手にとって分かりにくいのは当然だ。
3つ目。難しい言葉が1つもなかったとしても、なんの論理もない(筋が通らない)場合、理解しようもない。