Here are three issues that are difficult to fully solve:
1. Climate Change: It's hard to completely stop the negative effects of climate change, such as extreme weather and rising sea levels, even with efforts to reduce carbon emissions and use renewable energy sources.
2. Nuclear Disarmament: It's hard to get rid of all nuclear weapons in the world because some countries see them as a way to protect themselves, and it's hard to make sure everyone follows the rules.
3. Inequality: It's hard to make everyone equal in terms of money and opportunities because people have different abilities and make different choices, and some people might not want to give up their money or power to make things more equal.