Several signs help spot a possible bubble. A price-to-earnings ratio far above its historical average suggests stocks are overvalued. When prices pull away from the fundamentals — revenues, profits, real output — caution is warranted.

Watch for heavy borrowing. When buyers use debt to chase assets, the market grows fragile and the eventual fall gets harder.

Culture matters too. When your hairdresser is recommending stocks, people quit jobs to day-trade, and get-rich-quick schemes flood social media, those are classic late-stage warning signs.