How to Memorize

the root cause of the problem/fault/illness

Analysis

A root is the part of a plant which absorbs the nutrients from the ground. The root cause of something, therefore, is the basic foundation or the underlying cause of something. "This drug gets to the root cause of the illness and you can expect to improve within a matter of days." 

Social Examples (Basic)

1. The root cause of the airplane crash was a faulty computer system.
2. Doctors diagnose patients by looking for the root cause of their illness.

Professional Examples (Basic)

1. Our IT team has identified the root cause of the problem, so we should be able to push forward with production very soon.
2. Our aim here is to establish the root cause of the hostilities between these two parties.

Further Suggestions