Your brain had to think about pedaling, staying balanced, steering with the handlebars, watching the road, and maybe even hitting the brakes - all at one time. But eventually, as you got more practice, the neurons sent messages back and forth until a pathway was created in your brain. Maybe you got the exact toy you wanted for your birthday, and you're really happy. Or your friend is sick, and you feel sad and afraid. They all come from your brain, which controls all the emotions you feel.
Scientists believe that the amygdala is responsible for emotion.
So when you feel sad about a friend moving away, your amygdala is hard at work. But they're not all bad - the amygdala is also at work when you're really excited about winning your soccer game. It's normal to feel all different kinds of emotions, good and bad. Sometimes you might feel a little sad and wonder why. And sometimes you might feel anxious, or silly, or even frustrated.