I think of it in two ways and first is the external. This is the effects vices have on relationships as training partners, as people, and the sexes in the dojo. The second is internal and relates heavily to budo. To examine and recognize one's weaknesses; lacking emotional control or psychological stability, i.e. vices. To be aggressive and intent to over-come the weakness, i.e. having the mental discipline. Here in lies the modern sense of the samurai duty, and code, and conduct, bushido. The mental discipline.
Your warriorhood as an Aikidoka lies in winning over one's self. Mental discipline is metaphorically the sword that cuts the enemy. It is the ability of self-discipline to overcome personal vices that measures the character of the budoka. It is not the ease of which technical ability preformed by an Aikidoka that shows strength.
In combat, fights ( often on the losing end, but I had my share ), no one is undefeatable. Even the great Polumbus the Roman Gladiator was eventually slain. it is just that those who are said to be undefeatable knew when to quit. The real victory is the mental combat to over come weaknesses where a person can truly be undefeatable.
It all ties into having the mental discipline to over come the weaknesses i.e. vices that can bring harmony etc. internally and externally. And all of which is a part of Aikido; that is budo.