Doing good deeds, some like to leave their name behind, while others prefer to remain anonymous. Tan Shuchang felt he belonged to the latter category; however, because it involved his disciple who knew him well, he chose to conceal some of the benefits.
Of course, this act inevitably harbored resentment from the Karma Venerable.
After all, the Karma Venerable became who he is precisely because he had once mastered the Karmic Fire to an extreme degree. His defeat under the Karmic Fire gathered by Tan Shuchang was solely because the Karma Venerable himself had forsaken it.
Originally, this wouldn't have mattered much, but when Tan Shuchang employed the Immortal Technique "Water can carry a boat and also capsizes it," this undoubtedly greatly magnified the situation.
It led to the Karma Venerable falling into the Banhu Realm.