Can you explain quantum entanglement to me like I’m 5 years old?

The most upvoted comment is 100% wrong. That is not how entanglement works at all, at all.

Those two particles are in a superposition. It’s nothing — nothing even close — to the blue marble and red marble example. The state of the particles (or anything else in quantum entanglement) simply does not exist* until one of the pair is examined. Note that this is not me speculating. A Nobel Prize recently got handed out for demonstrating facts directly related to what I’m talking about here.

What this means is that an entangled spin-up and spin-down electron pair, no matter how far they are separated, do not collapse into their respective spins until one of the pair is examined and it assumes a spin orientation. Then the other instantly does the opposite as well. In the top-voted commenter’s example, one marble is always red and one is always blue. This is completely not the case with entanglement. Entangled unexamined electrons are neither spin-up nor spin-down, but can only be represented by a probability calculation. To be perfectly clear: this is a fact of the universe, this probability, not something we are using due to lack of knowledge. The superposition is a feature of the universe itself, not of math or resulting from lack of understanding.

It’s ok, though. I’ve talked to actual physicists who don’t really understand entanglement, so I wouldn’t expect some random Reddit commenter to make sense of it either. Your macro intuitions just do not work at all for anything quantum. It’s better just to think of it as is, not as we wish it were.

*Other than as a probability inherent to the universe; not probability as we are accustomed to thinking of it, used due to lack of knowledge.