Learning about the existence of these HeLa cells was an emotional and difficult experience for the family.

VOA: special.2010.07.21

Learning another language is incredibly difficult.

学习另一种语言是非常难的。

学外语的时候 - SpeakingMax英语口语达人

Most of what makes learning difficult is specialized language and it usually takes me five books to begin to have a feel for this language.

FORBES: How To Learn Anything In Five Not-So-Easy Steps

Society seems obsessed with celebrity, fame and trivia while serious learning and difficult achievement take second place.

CENTERFORSECURITYPOLICY: From fashion to fortitude: the road to resilience

And the dangers of aversion to difficult learning should not be underestimated.

CENTERFORSECURITYPOLICY: From fashion to fortitude: the road to resilience