Root cause,

Definition of Root cause:

1. Agent, failure, or fault, from which a chain of effects or failures originates.

How to use Root cause in a sentence?

1. I didnt now what the root cause was for the mans betrayal of his friend, but I knew that there was something going on.
2. The fabrication line in the main factory, which produces the initial components, was found to be the root cause of all production units being denied for the last week of December.
3. If you want to try and change things up you should look for whatever may be the root cause to the problem.