When my Brother in law was about 55, he had his whole retirement in xerox, he worked there his whole career. Lots of $$ built up when the stock was at $150. Then it crashed. He rode it down. When it was at about half, of what it was he bought more, all he could afford. then it went all the way down under $10. He was wiped out. He worked well into his 70's before retiring. Now, 20 years later, Xerox has never recovered. THere is no guarantee that if you ride your stocks down that they will ever recover.
I paid attention. I'm 60, I want to retire before I turn 75. If I see trouble, I'm getting on the sidelines fast. I don't lose anything by taking a profit and sitting out. I lose POTENTIAL profit, but I also shield myself from potential loss.