"人生で一番悲しい感情は、とても楽しそうに踊っているときに、もしかするとそうすべきではないと気付いたときだといつも思っていました。"

Simplified Meaning:

Sometimes, we can be very happy and enjoying a moment, but suddenly feel doubt or regret. Imagine you're at a party, dancing and having fun. Everything feels perfect. But then, you remember you have a big exam tomorrow, or maybe you had an argument with a friend earlier. That joy gets mixed with guilt or worry. Think of a child who gets a new toy but knows their friend didn't get one. They feel happy but also a bit sad for their friend. This mix of feelings happens in life when something good clashes with a reminder of something less happy or important. It's important to find balance. Enjoy the good moments, but also be mindful of your responsibilities or the feelings of others. This helps you appreciate happiness without ignoring other parts of life.