Mark Cuban bought a luxury home originally worth $25 million for just $12.5 million, after the previous owner had only lived there for 8 months and was hit by a stock market crash and liquidity crisis. No matter how good the paper gains look, it’s useless; holding on without selling, in the end, you can only cut your losses drastically and dump the property.
When the market is good, everyone thinks they see through the cycle; when the trend reverses, they realize that unrealized gains are ultimately just numbers. Taking profits and controlling positions are more important than anything else.