What does it mean that they all lived with lifelong regrets?

Eighteen years after his transmigration, Lin Wuhua was admitted to the National Extraordinary University. However, because he refused to give up his place, he was falsely accused of being a "reincarnated infiltrator" and imprisoned in a heavily guarded medical facility, his life hanging by a thread. Fortunately, he unexpectedly activated the "Book of Reincarnation"—by experiencing different lives and completing tasks, he could help the native world integrate external energy and receive rewards from the world's subconscious. Thus, he became a disciple of the Sword Sect, twice shattering his own sword bones to deduce the "Heart Sword Technique" from scratch, enabling the Ice Sword Master, who had strayed onto the path of ruthlessness, to become the First Sword Immortal. He became a disciple of the Weapon Sect, sacrificing his spirit and heart, spending his entire life infusing souls into puppets, giving lifeless beings human emotions. He inherited the last lineage of the Demon Blade, fusing the power of ten thousand demons to create perfect blood, using chaotic spirits as a foundation to create the strongest perfect demon in the world. In each reincarnation, Lin Wuhua had a clear conscience, doing his best to achieve his goals. But... why did their reincarnations all come to this world? I only have the mental techniques, but no actual cultivation? What am I supposed to do? — Get fucked?