Not just anything could be judged as weakness by the curse, though. Any weakness must be an attribute or characteristic of the target that's smaller, poorer, or weaker than the corresponding attribute or characteristic in the user of the Death Declaration Ability.
In order to fulfill this request, the curse began to compare their attributes. It compared their strength, speed, defense, total power output, and the level of injury on both sides.
As it turned out, Loki had exactly the same amount of strength, speed, and defense as the black monkey. This meant that he wasn't weak in this aspect. The same was true for the power of his mind, will, and soul.
Next in line was the comparison of their total power output. Loki aced this one because he was currently producing more power than the black monkey.
Then their level of injury was compared. The black monkey had more Entropy than Loki, so Loki also won this comparison handily.
