This problem is not so difficult as it seems.
That problem wasn't that difficult to solve.
It's difficult for me to solve this problem.
This problem is too difficult to deal with.
This problem is difficult to solve.
This question is infuriatingly difficult.
It is difficult to solve this problem.
This problem is difficult to solve.
The problem is too difficult to solve.
That is where the difficulty lies.
Applying that to this phenomenon is difficult.
That exercise was difficult, but this is still more difficult.