Envy

Standing up, Cain felt his joints crackle with power, sounding like miniature thunderclaps. 

The rush of energy filled every inch of Cain's body. And yet, his mental state was no longer largely swayed by this.

During all of his training, he felt his Martial Heart passively become firmer. Each passing day, he can feel his Martial Heart subtly grow, allowing his comprehension session to last far longer.

From the growth of his Martial Heart, Cain was increasingly calmer and more critical. As he experienced these growths, a thought swirled around his mind. 

Is the growth of one's Martial Heart the same for everyone?

It was curious to consider as Cain was positive that not all powerful cultivators have a calm and critical personality type. Hell, he's fully aware that for some, the more powerful they grow, the narrower their mind becomes.

To him, this was also understandable.