Worry is an attempt to solve an issue that has an uncertain, and possibly negative, outcome.

An important point here is that worry is a combination of cognition and affect, a process that engages both our intelligence and our emotions — and the problem with trying to interrupt it is twofold.

• Intellectually, worry causes us to involuntarily repeat unpleasant and unproductive thoughts, thoughts that do not contribute to effective problem-solving but cyclically feed on themselves. And trying to silence a recurring thought is a lost cause, thanks to a cognitive glitch known as the "thought suppression paradox."
• Emotionally, worry is most directly related to fear; more specifically, what affect theorists define as the "affect" of fear, an evolved set of automatic psychological and physical functions that emerge to guide our behavior when we are confronted with anxiety. Unfortunately, affect is not always appropriate or helpful.

An argument with a worry is an argument you can't win: when you tell yourself not to worry, you aren't going to silence it — you're engaging the worry in conversation, inviting it to explain itself further.

Worry causes anxious, repetitive thoughts — but if you concentrate on stopping those thoughts, you are actually directly contributing to them. Worry develops from and perpetuates a state of fear — but forcing yourself to suppress a negative emotion can instead magnify it, or activate other negative affects like anger or despair.

Since we cannot stop worrying through conscious effort, the best course of action is to concentrate on working around it. 

• Accept worry, acknowledge the stressors and limitations it has imposed on us, and focus pragmatically on achieving the best possible outcomes under the circumstances. 
• Instead of trying to stop worry, treat it like a headache, or a sprained ankle: it may hurt, and it's going to mess up your day, but no matter what you do, it's not going away immediately, and fixating on it will probably make it worse.