It is simple to be fat but difficult to be strong.

发胖很简单，强壮却很难。

youdao

Like most students, when studying at middle school, I found math interesting but difficult, which was a challenge for me.

像大多数学生一样，读中学时，我觉得数学虽有趣但很难，这对我来说是一个挑战。

youdao

Foil wrapping paper is beautiful but difficult to use.

锡箔包装纸好看却难用。

《柯林斯英汉双解大词典》

But for people who have a difficult time controlling their movements, this little navigational issue can be a really big problem.

VOA: special.2011.04.18

But it's a difficult claim because even as Milton makes this claim, he manages to undermine its force.

但这是困难的，因为即便是弥尔顿做出了这一宣告，他也打算降低它所蕴含的威力。

耶鲁公开课 - 弥尔顿课程节选

A little indirect but not so indirect that is difficult to understand. You should use this often.

有一点委婉，但不至于委婉到让人难以理解。应当尽量多使用这种句型。

Why don't 课堂 - SpeakingMax英语口语达人

Be forewarned that the film is not only violent but difficult to get into.

WSJ: Spielberg Comes Home

Identifying the world's greatest male athlete turned out to be easy to argue but difficult to answer empirically.

WSJ: The World's Greatest Athlete?

This is fuelled by liquid hydrogen, which is powerful but difficult to handle because of the low temperatures involved.

ECONOMIST: Sayonara, spaceflight?