Although refining the Marrow Cleansing Pill also required two steps, and the quantity of medicinal herbs he needed to refine at one time was still within his controllable range, the prolonged duration of refining posed a major obstacle. Once his stamina and focus failed to keep up, it would easily lead to failure in the subsequent "pill amalgamation" step.
This was precisely one of the primary reasons his simulated alchemy attempts had failed.
Up to this point, he had indeed succeeded a few times during his simulated alchemy sessions. But compared to the number of failures, those successes were practically negligible.
Chapter 962