Spoiler test of depth
The spoiler test of depth states that if something can be "spoiled" by spoilers, then it isn't deep, or in other words, that truly deep things cannot be spoiled by giving away some secret.
The spoiler test is distinct from saying "I like to read spoilers before watching a movie/reading a book" (i.e. the related question of whether one would like to hear spoilers before consuming a story). (If you search online about discussions about spoilers, this is usually the thing people talk about.)
I notice that in math, I often want to be spoiled -- I want to understand something, and I want people to tell me the answers. That doesn't mean that I won't eventually try to re-derive everything from scratch. When someone explains something in math really well, or comes up with a novel way to explain something, I'm glad that I heard about it, rather than being upset that it has been spoiled for me.
There is this thing where if you hear the answer, you don't appreciate the answer, so you learn less. That's definitely a thing. In practice, this isn't really a problem since people forget things all the time in math. But another reply is that someone could "spoil" something in math even further by explaining how they came up with the answer. In that case, you would be able to appreciate the answer, and that seems like a good thing.
I started having thoughts along these lines because Jonathan Blow often mentions spoilers (especially when talking about The Witness), and how he doesn't want to spoil the game for people. I think I have a disagreement or a personality difference with him. The disagreement isn't whether enjoyment from playing the game will be diminished by reading analyses about the game and watching let's plays -- I think we both agree that doing that does diminish the enjoyment you get. Rather, the disagreement is about whether a game whose enjoyment can be diminished in such a way is even worth playing in the first place.
Why should spoilers have anything to do with depth? I'm not quite sure. But I think it has something to do with "replay value", and how truly great things can be consumed over and over again (sometimes delivering greater enjoyment on later iterations). If an idea is deep, you can't really comprehend it in the first attempt; you need to keep coming back to it over and over again, to "attack" it from different angles and see it in a new light (say if you come back to it after having learned more about some other topic).
If something can be "spoiled" by a spoiler, that means there's this one trick to it, one secret where once you have that secret, it gives away the purpose of consuming it.
I think this also explains some fiction consumption preferences that I have. I usually don't like stories with plots in them. Plots are basically the thing that gets spoiled by spoilers.
Similarly with people -- a person who is actually deep cannot be spoiled by finding out their "mysteries". They can't hide behind some aura of mystery to seem more interesting (which is something that can be spoiled). A person who is actually interesting still seems interesting even after you've found out all the things about them. Even when you get to know someone so well that you have a pretty good simulation of them in your head, you're still surprised often enough in delightful ways that makes you want to keep interacting with them. You still regularly learn new things from them even if you've known them for many years.
This post makes a similar point: https://medium.com/humungus/spoiler-madness-d48340e9233d
Vipul points out a connection with the "curiosity gap", which is the thing where people lead you on without telling you the secret. This is another thing I don't like.