Opening an Umbrella Inside
There is a thought that this is actually where the superstition came from. The introduction of the mechanical umbrella happened in the Victorian Era in England. The first versions of it were made with stiff steel poles that, when opened indoors, could cause major injuries like cuts and possible eye loss. While that might be the case, the superstition goes all the way back to the ancient Egyptians who also had umbrellas, though back then they were parasols, made for blocking the sun instead of the rain. If you were to open one indoors, where there was no sun, it was considered an offense against the sun god, Ra, who would curse you for it.