When observed, quantum waves collapse and become the particles that make up reality. By being observed, things become real. The answer to the question - 'if a tree falls in a forest and no one is there to hear it does it make a sound?' - is 'nope'. For something to exist, another existing thing has to know it exists. To exist you have to be observed. 'Esse est percipi.' Bishop Berkeley said it, the Australian Aborigines always knew it, and now the rest of us are beginning to understand it. I think it's all got something to do with this: (ψ = Σanψn).
OK, you got that? I've made it real simple for you because you're real simple. You understand? Good. Even if you don't understand, don't worry because I probably have it wrong anyway. If you do understand then don't worry if I have it wrong because either way you're none the wiser so it doesn't really matter.
Anyway, this brings me to Alan. Alan was born to a reclusive single mother in a remote barren quarry where the two lived out their whole lives. Alan's mother survived by trekking daily to the nearest Lidl, which was ages away, and coming back with food and supplies for herself and her son. Don't bother asking why she chose to live like that because no one knows the answer, just like no one knows the answer to why you choose to live the way you do. You don't even know the answer to that one yourself.
So, Alan's mother never told anyone she had a son and she was the only thing that knew he existed. That was fine but one day she died leaving Alan with nothing remotely sentient to vouch for his presence in reality. The fact that he could observe himself wasn't enough to help him and he gradually faded away. His eyes faded away first so he didn't even get to see his hands and limbs and torso vanish. The last thing to go was his mouth. It issued a scream, a horrifying shriek of sheer fear, that no one and no thing ever heard because, in a way, it never happened.
You might consider it sad about Alan but don't. From what I hear from those who never knew he existed, he was a bit of a dick. I can't say the same for my Uncle Stan though. He was quite a nice fella but very boring. He'd just sit in the corner mumbling about some boring topic like rhubarb distribution in late nineteenth century Prussia or what he had for breakfast that morning and how long it took him to make it. Stan was so boring everyone stopped listening to him and gradually forgot he was there, including his wife and parents and even his kids. Stan faded away as if he never existed, just like Alan. No one was the wiser and no one shed a tear as he mumbled his disbelief and slowly faded from existence, just like a radio station vanishes as you turn the dial. One second the DJ is talking inane shite about this and that and the next second the fucker is gone as if he was never there at all.
The same will eventually happen to the rest of us. We live a while and then die but continue to exist as memories but then, over generations, we are forgotten and, over billions of years, any evidence left of us erodes and crumbles to less than atoms and then these less than atoms cease to be when the Universe finally pops out of existence. It'll be as if none of us were ever here because there won't even be a 'here'. Are you horrified? Do you feel like screaming as Alan did? I don't. I actually find the thought comforting. Especially when I consider the fool I made of myself in front of everyone when I got drunk the other night. The thought of those events being utterly erased from existence suits me fine.