Lack of progress

Sure, here is the translation:

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That's when the pain began. Athos didn't understand what was happening but felt it was dangerous to continue and stopped immediately. It was different from the pain he felt whenever forming a new layer.

It was something more intense, causing a sense of danger, as if he was doing something wrong and taking a step in a perilous direction.

Without understanding what he was doing wrong, Athos tried repeating the process several times, but the result was the same.

It had been weeks since Athos isolated himself in the laboratory, yet he hadn't made any progress. He had already discarded the human technique as useless and tried his own ideas, but nothing worked.

"What the hell am I doing wrong?" Athos was sitting on the stone floor of the testing area, pulling his own hair in frustration only for it to fuse in his hands and grow back again.