A more nuanced view would be “don’t fight the tape unless you have a good reason.” There is usually a reason why stock prices react the way they do. If you believe that reason has become obvious and that the market has moved past the “fundamental” momentum stage and into the “technical” one, then buying a stock that has gotten beaten down to below its fair value can be a very profitable strategy. But make sure that you really understand the business and have a good reason for thinking that it will be worth more in the long term than it is today. This is why Buffett only owns a small and concentrated portfolio of companies with relatively simple businesses that he can understand.

“Fighting the tape” can be really dangerous because there is always a strong chance that somebody who is selling knows something that you do not. They might even be aware of non-public information. For most individual investors who do not have the time to really understand a business in as much detail as professional investors such as Warren Buffett, it is probably better to wait for a stock price to stabilize for a couple of months before rushing in and buying (e.g., look for a chart that has flattened out and is no longer falling).