There are many hacks that we only learn later in life, and wish we had known about years ago. People often share such hacks when they learn them, saying they felt like they were “today years old” when they finally learned them.

We were astonished when we learned this hack about Christmas lights–it seriously might make you want to sit down.

If you’ve ever opened a box of Christmas lights to find a single, red light, then you know where we’re coming from. You probably assumed that it was just an extra in case one of the white bulbs burnt out. The bulb has always been red, and we never thought to question it. Christmas string lights last much longer than one would think.

A TikTok user was today years old when she learned the spare red light’s true purpose. She shown what happens when you actually use this bulb.

She first held the red bulb to the camera lens for a close-up view. Against a backdrop of white Christmas light supplemental description: We see shimmering Xmas lights around the garage door.

Subsequently, she walked over to the white lights and unplugged one of them. The strands of lights went dark because that’s what happens when one light burns out all of the others follow suit. That’s partially why there is always a spare red bulb in the box, right? Well, kind of … but not really.

Finally, she puts the red light back in its place. The lights come on again, but that’s not all. Watch the video below to see what else happens when you use a red Christmas light.

@viznelly **I** didn’t know. 🤩🎄☃️ #christmas #diy #home #homedecor #christmastiktok #christmasdecor #houseoftiktok #cleantok #housework #hometiktok #holiday #tips #hacks #hacksandtips #christmastree #navidad #feliznavidad ♬ It's Beginning To Look A Lot Like Christmas – Bing Crosby

Are you surprised? Many viewers were astonished by this tip and had no idea that the red light was for this purpose. One person said, “Dude all they had to do was write that somewhere on the box. I wasted so many years not knowing about this.”

Another person added, “The blinky lights are nice but having one red bulb would bother me.”

Many viewers were already familiar with this tip, sharing that they assumed it was “common knowledge.” How is this possible? There’s nowhere it says to do this included in the directions. One person said, “As someone who grew up in the 90’s…I thought everyone knew this.”

Another person stated, “Ppl saying ‘Omg I thought this was common knowledge’ as if it makes an oz of sense that putting a diff bulb in makes sht blink.”

Christmas lights are often more festive when they blink. Maybe you should go grab the red bulb out of the box and see if it makes your Christmas lights blink!