It is late at night, and your body feels very tiredtired/ˈtaɪərd/L1疲劳的，累的feeling that you want to rest or sleep. Your eyes are heavy, but your brain will not sleep. Many people call this being “wired but tired”, and it feels strange and frustratingfrustrating/ˈfrʌstreɪtɪŋ/L2令人沮丧的；使人懊恼的making you feel annoyed or upset because you cannot do what you want.
A long time ago, the brain stayed awake when a tiger or dangerdanger/ˈdeɪndʒər/L1危险something that can hurt you or cause problems was near. It made the body ready to run or fight to stay safe and alive. This was a very good plan for a dangerous world.
Today, the world is different, but the brain still uses this plan. Screens, phones, and worriesworries/ˈwʌriz/L1担忧，烦恼thoughts that make you feel unhappy or afraid about school and work keep the brain busybusy/ˈbɪzi/L1忙碌的having a lot of things to do. The brain thinks there is danger, so it stays awake and busy all night. A tired body with a busy brain is common, but it can be hard.
