His father says he knows that the transplant issue is a difficult one for families.

CNN: Boy not allowed to get life-saving transplant in Japan

Trying to answer one issue in isolation can be difficult.

FORBES: Fee-Only Financial Planner: What's the Difference?

"I should make it clear that we always understood that the photographs issue would be a difficult one for the IRA, " he said.

BBC: NEWS | UK | Northern Ireland | 'Arms photo reasonable': Ahern

Second, the issue of combined sewer overflows is one of the most difficult water-quality issues faced by cities with old infrastructure like New York City.

FORBES: Sustainability Lessons for the Big Apple

One of the problems concerning legislation on the issue is that stress is a difficult condition to diagnose and correct.

BBC: Stress at work: the pros and cons

On that issue there is progress, and it's also the most important one, maybe the least difficult one of the lot.

NPR: Benchmarks for Iraq Deemed Divisive