The most greatest struggle we all face is between feeling and thinking. The feelings are controlled by amygdala, and it operates subconsciously. The thinking, on the other hand, is controlled by prefrontal cortex and operates consciously.
There is no greater battles than these two.
During any argument, you’ll often notice a physical response similar to how to react to fear, which is sub-consciously. Recognizing that, your conscious mind can deny it. The reaction from the subconscious mind comes in spurts as a trigger, while the reaction from conscious mind (pre-frontal cortex) is more constant and gradual.
The greatest are those who acknowledge and reflect on what causes their sub-conscious mind to react and what can be done about it. And this is obviously the greatest struggle of human kind.