The greatest is not undefeated
In life, there is the battle and then there is the war. The battle is singular but the war is plural, made up of many battles over time.
People like to boast of being undefeated in battle, and yes those battles are important, but it is more important to win the war.
The greatest is not one who has never been defeated in battle, in fact, one cannot truly claim greatness if they have never been tested with failure and overcome it.
Some people only choose to fight where they know they can win. They never try to do anything bigger than they can handle. They always play it safe. It is more important for them to remain undefeated than to learn and grow.
Greatness accrues over time, it is the attitude of one who looks beyond winning temporal battles and focusses on the ultimate aim of winning the war.