The phrase "difficult task" refers to a challenging or demanding activity that requires significant effort, skill and persistence. It may also imply that there are obstacles or complications involved in completing the task successfully.
Getting a child to sleep can be one of the most difficult tasks of parenting. (parents.com)
But at present it is not very difficult task for us. (adultfindout.com)
I am so much in love with it, it has solved my most difficult task of applying and blending my concealer and then setting my under eye with a powder. (beautyandblush.com)