It is like this: there is a continuous current of chatter happening in you twenty four hours a day, seven days a week. From this current a few spikes rise. These spikes are what you feel and express as worries. Worries are nothing but spikes in the current of thoughts constantly moving within you.
These thoughts are mostly negative. That"s the problem. If I ask you to write your life story in a few pages, you will write a few incidents highlighting how and when you struggled. You will not highlight the many joyful incidents that happened in between. The mind is trained to record only negative things. Even when something joyful happens, you remember only the moment when it ended, never the moments when you felt joy. Because even when you are at the peak of joy, you are always worrying about when the joy will end! The mind is trained from a very young age to think that life moves from one worry to the other or from one pain to another, never from one joy to another.