Once upon a time, a long time ago, there was a bunch of countries in Europe. One of the countries wasn't doing very well. It was very sick and had a lot of problems. So the other countries started calling it the "sick man of Europe."
Just like when you get sick, the "sick man of Europe" had problems with its body. Its government was very weak and couldn't make good decisions. Its economy was also doing very badly, which meant people didn't have enough money to buy things they needed.
The other countries tried to help the "sick man of Europe" by giving it some medicine, which is like help, to make it feel better. But it took a long time, and the "sick man of Europe" had to work really hard to get better.
And that's the story of the "sick man of Europe." Just remember, when someone is sick, they need help to get better, and it can take a lot of time and effort to get better.