Your tech stocks may bear winnowing, too, not to mention the many blue chips that look sick. You also might want to sell a losing mutual fund. You can't be sure, of course. Maybe your losers will bounce back, big. But then again, maybe they won't.
Investors often find it hard to sell a stock they have lost money on, even for a tax advantage.
Selling it cuts the cord of hope. Emotionally, you believe that the stock must be worth at least as much as you originally paid. Some stocks never come back. Some recover only after many years. While you're holding the stock, in order to prove a point, the rest of the market may pass you by.