Stocks are in an AI-driven bubble that could end in a crash of 50% or more, which is bad news for buy-and-hold investors but manageable for anyone willing to follow a simple sell rule.

• History shows the stock market has crashed by half or more several times, and the AI boom looks like the dot-com bubble all over again.
• Buy-and-hold sounds safe, but someone who bought at the 2000 top waited 14 years just to break even — before counting inflation.
• The simple fix: sell when price falls under the 200-day moving average and that average turns down, then buy back when price climbs above it and the line flattens or rises.
• The same rule works on gold and Bitcoin, which fall 50% or more on a regular basis — it would have dodged the 2022 Bitcoin crash and the 2013-2016 gold slump while keeping most of the gains since.

Outlook: If the AI trade cracks, investors with an exit rule keep their money while buy-and-hold savers ride it all the way down.