At Meng Qi and Qing Yu's level, spirit momentum was considered the most crucial element that determined a battle. A person whose spirit was suppressed or heart was flawed could only exert less than 60 or 70 percent of his power most of the time. Both of them would be doomed even if the disparity in power was only 10 or 20 percent. After all, everyone had their trump cards. If either of them could seize their opponent's flaw and use it to attack without reservation, they could kill their opponent in just one round of fierce attacks without needing to use their killer moves.
Then there were the countless mystical arts. If his opponent had a deadly flaw in his mind, Meng Qi could defeat him with his Peace Quietude Split, Mortal Dust Fall, and even Supernatural Power of Shaking Heaven and Hitting Earth.
Of course, that was a different case for those practicing demonic arts. The more negative his emotions were, the stronger he would be.