There are always people who know what is going to happen before it happens and they either start selling or buying ahead of the event, or rumours are triggered and people in the loop take early positions. If enough people buy a stock, its price will go up (usually), due to the simple law of supply and demand. If enough people sell a stock, its price will go down.
There will always be trading opportunities, so be patient and strike. Find out what works best for you and make a habit of doing your homework. You’ll trade more decisively and reap the benefits of daily preparation!
Good luck and safe trading