That's not only bad investing, it's bad merchandising. A good trader knows that the customer's the boss. If the trading floor's screaming for new stocks you sell them stocks and pile up cash. When they're crying for cash for their stocks you oblige by meeting the need.
Yes, years ago business professors (often with their own private-sector gigs) described how the psychology of the market defied logic; people tended to buy as it soared and sell as if fell - almost guaranteeing they’d lose their shirts.