Learning the Chinese language was a long-term and difficult endeavor.

This is a difficult endeavor, with far-reaching and still uncertain consequences.

And why is brain surgery alone emblematic of a difficult endeavor?

For me, a woman no longer young whose walking is confined to city streets, it loomed as a difficult endeavor, especially in 105-degree weather.

This cold startup with no outside support was a difficult endeavor.

This is an incredibly difficult endeavor, but the Iraqis are moving forward.

In the not-too-distant past, counterfeiting was a difficult and expensive endeavor.

This is a difficult endeavor when working with living plants and animals.

Learning a second language can be a difficult and frustrating endeavour.

The expedition turned out to be a difficult and exhausting endeavor.