Because I'll never remember this.
https://www.imore.com/how-to-troubleshoot-reset-airpods
If you see no light: Your AirPods and their case are dead and need to be charged.
If you see an amber light and your AirPods are in their case: The AirPods are charging.
If you see a green light and your AirPods are in their case: The AirPods are charged.
If you see an amber light and your AirPods are not in their case: The AirPods case has less than one full recharge remaining for its AirPods.
If you see a green light and your AirPods are not in their case: The AirPods case has at least one full recharge remaining for its AirPods.
If you see an amber light while your AirPods are connected to a charger: Your AirPods are currently charging.
If you see a green light while your AirPods are connected to a charger: Your AirPods are fully charged.
If you see a white flashing light: Your AirPods have been reset and are ready to connect to your iPhone, iPad, Mac, or other device.
If you see an amber flashing light: Your AirPods have encountered a pairing error and you'll need to reset them.
If you see a green flashing light the airpods are in an unrecoverable error state and you need to factory reset the airpods. Put them both in the case without closing the lid then press and hold the pairing button on the back of the case. It should start flashing white. Keep holding the button for about 15 seconds until it switches to flashing orange. Your airpods are now reset.