ELI5: How do bad emotions make good emotions better?

Bad emotions make good emotions feel better because our brains need contrast to truly notice and appreciate happiness.

Imagine if you ate your favorite chocolate ice cream for breakfast, lunch, and dinner every single day. At first, it would taste amazing! But after a few weeks, it wouldn't feel special anymore. You might even get tired of it. But if you have to eat bitter broccoli for dinner, that scoop of chocolate ice cream the next day tastes like the best thing in the whole world.

In psychology, our feelings work the exact same way through three big ideas:

• Emotional contrast: You cannot understand how warm a cozy blanket feels until you have stood outside in the freezing rain. Feelings like sadness or fear are the "cold rain," while joy and relief are the "warm blanket." Without the cold, the warmth is just normal.
• Appreciation and gratitude: When you feel sad because you lost a toy, it teaches your brain how much you cared about it. The bad feeling shows you what matters. So, when you get the toy back, you feel double the happiness because you remember the pain of missing it.
• The feeling of relief: Think about how your body feels right after being super scared by a loud thunderstorm, and then the sun comes out. That huge wave of peaceful, happy calm is called relief. You can only feel this deep type of happiness because you were scared first.