When I went back to C++ after learning Rust and used a vector again, I realized this and it hit me like a brick. I used to program in C++ before, so it wasn't like I didn't know this, but it was something rather unremarkable to me. Then I go back to C++ and throw vectors around willy-nilly and stuff works. Huh, I thought, this feels strange, I wonder how C++ accomplishes this without a garbage collector or ownership. Then it hit me -- it deep copies All The Things. Again, I already knew this, but I hadn't ever thought about it much. But the change in perspective made it stick out like a sore thumb.