When we compare martial artists, we typically compare their inner power and fighting techniques. Sometimes, we even compare their intelligence and strategy. One thing we don't talk about very much, however, is the fighters' mental affinity. Having great inner power and great fighting techniques and even great intelligence does not necessarily mean that one has great mental affinity. Mental affinity is toughness of mind (which is related to courage, but not the same thing). Fighters with weak mental affinity are easilly "psyched out" even by weaker opponents, and can be readily goaded into making mistakes or reckless moves in battle. Fighters with strong mental affinity, however, are very difficult to psyche out because their minds are as strong as their bodies.
Strong fighters who have weak mental affinity include the Golden Wheel Monk, Kau Cheen Yan, and Mo Yung F'uk. The first two have Greats-level inner power, and all three have Great to near-Great fighting techniques. All three, however, have huge ego and pride issues, and this often causes them to make mistakes in judgment that opponents can exploit. Often, they'll use the wrong strategy against an enemy...or defeat themselves because their hesitation (due to fear of defeat and humiliation) causes them to lose the initiative.
Fighters who have strong mental affinity include Kiu Fung, North Beggar Hung 7 Gung, and Gwok Jing. They too are proud men, but their egos do not rule them to the extent that they can be easily led into making mistakes in battle to protect their egos. These fighters are extremely determined to accomplish their goals, and have no fear of sacrificing themselves in the process. They are extremely focused and very difficult to psyche out.
There is a different group of fighters with strong mental affinity that comes not from extraordinary willpower or determination, but from a centered, calm enlightenment. They are above fear and above petty emotional manipulation. The Janitor Monk, Central Divinity Wong Chung Yeung (post-Lam Chiu Ying), and Cheung 3 Fung fall into this category.
Then, there is the fighter whose strong mental affinity does come from superior intellect. They are difficult to psyche out or goad into recklessness because they are very calculating, and likely several steps ahead of the opponent both mentally and physically. East Heretic Wong Yerk See, Wong Yung, and to a lesser extent, Yeung Gor belong to this category.
Finally, there is the carefree fighter...who is so naturally freeform and chaotic that any effort to break him down mentally would be in vain. Chow Bak Tung belongs to this category.