I have a question regarding holding knowing a company is going to decline but go back up again.

I always see people say to hold when a company is about to decline because they know that it will go back up. What is the point of this? Lets say you have $1000 for 2 shares in company X and it is likely going to go down to $350 a share then back up to $600. In that situation I see a lot of people hold it but wouldn't it be better to sell and buy it again with the same amount of money when it goes down to $350 because then you paid the same amount but you are getting more shares in the company,