Earlier quoted context omitted.
Stock values go up when people buying stocks expect them to go up. Stock values go down when people holding stocks expect them to go down.
Why would you hold a stock if you think it should go down? If you think the stock is valuable but in the near term should go down, why not sell and then buy in increments as it goes down?
Tax reasons might be one as well, long term capital gains are taxed less.
There are few investors that can spend the time it takes to be active like that.
Most people buying individual stocks are better of buying ETFs anyway.
In the end it's a choice on what to spend your time on.