Let's look at what the word worry means
According to wikipedia - Worry refers to the thoughts, images, and emotions of a negative nature in a repetitive, uncontrollable manner that results from a proactive cognitive risk analysis made to avoid or solve anticipated potential threats and their potential consequences. Worry is described as a response to a moderate challenge for when the subject has inadequate skills. Worry turns to be problematic if one has been excessively apprehensive more days than not for at least six months.
But why do humans worry?
Humans are used to worrying just because they have negative thoughts on something which is constantly hunting them down, it's like having a nightmare which is constantly in your mind and you can't get off it, maybe something bad happened to you or someone you care about got sicked or something else terrible happened to them.
Example of what happened to me recently
I recently moved to a country in Africa, it's my fatherland named Ghana, I haven't met with any of my family over there and didn't go to my city instead I went to the capital - Greater Accra. I moved in with a sister and two of her friends and it's been few months after spending all my cash, I was told to move out within a week, which made me worry so much for a night. Then I stumbled up a gif that changed it all.
This is a flowchart of life worry
Do you have a problem? -----------> No -------------> Then why worry?
Do you have a problem? -----------> Yes-------------> Do you have a solution to it? ---------> No ----------> Then why worry?
Do you have a problem? -----------> Yes-------------> Do you have a solution to it? ---------> Yes ----------> Then why worry?
So why do you still worry?
Everything ends up to don't worry about it. Worrying won't fix any problem or stop bad things from happening, instead it stops you from doing good or what's next.