I really liked the simple explanations in this recent Scientific American article by Matthew von Hippel about vacuum decay: https://www.scientificamerican.com/article/the-end-of-the-universe-could-begin-with-a-quantum-bubble/ (archive: https://web.archive.org/web/20250524071625/https://www.scientificamerican.com/article/the-end-of-the-universe-could-begin-with-a-quantum-bubble/)

(I thought of it metaphorically like sand in Minecraft, which can generate floating in the air but suddenly collapses when, say, the player breaks a block or places a torch. Except the sand is, like, the laws of physics.)