Limited by the conditions on site and unable to disturb the Elf Empress, Chu Fei had no way to bring out a Quantum Computer for simulations. He could only calculate it himself in his mind.
Mental calculations were certainly slow, but they were also a necessary step in verifying a cultivation technique.
Computers were forever only tools. Whatever capabilities a computer possessed had been manually programmed. It was not that computers could not evolve new capabilities of their own, but those capabilities still evolved based on conditions input by humans rather than through completely autonomous evolution.
Creating something from nothing was an ability unique to intelligent life. Computers today did not yet qualify as life, much less intelligent life.
In short, conducting simulations in his own mind allowed him to spot certain logical errors in the cultivation technique—but humans themselves were sometimes prone to logical errors. Cognitive traps, for example.
Humans had tendencies to make mistakes every moment of every day. They simply possessed powerful self-correction abilities, so very few of those tendencies ultimately manifested, and even fewer caused serious consequences. But their existence remained undeniable.
How did so many bugs in computer systems come about? Errors in the code. There might be only one mistake in tens or hundreds of thousands of characters, yet every character then had to be inspected from the beginning. That was why engineers became "siege lions"—bald geniuses with only a ring of hair around their heads.
A Big Data Cultivation technique was incomparably complicated, involving billions upon billions of lines of code. From Chu Fei's first day of cultivation until now, the various codes he had accumulated had reached an unimaginable quantity. Even calling it as vast as the sea might not be enough, because there were also mountains of crappy code in there.