Their definitions aside, I think that the word difficult shows more negativity than the word challenging. Saying something is difficult shows a defeatist attitude while saying a task is challenging shows a positive attitude or tackling it head on despite the “difficulties”.

Have a star, sweetie.

Challenging on the other hand stirs a competitive perspective. It makes you think that the issue CAN be solved, though it will take much time and effort. It gives you a positive impression of a task or whatever it is that’s challenging.

Another person might be difficult to understand. No challenge there, but not easy either.

Challenging assumes a “conquer it” attitude that makes a big task seem worth the risk.

challenging – something I must do and will gain or improve by doing

difficult = changing a tire in the rain without a jack

challenging = learning to drive