Noticing the anger of his allies, the Hand of the Heavens was quite embarrassed, but still patiently explained, "I just had an outbreak of injuries, and under the tremble of my hand, I mistakenly cast a Feng Shui Spell as a Thunder-Water Spell,"
This reason seemed plausible because wind and thunder are indeed very similar; wood yin is wind, rice yang is thunder. In the hand seals, one is upwards while the other is downwards. It's not impossible to make a mistake if one's hand trembles and the wrong seal is pinched.
However, the matter wasn't that simple.
The Curse Mark isn't something that Dan Dan can activate with just a hand seal; it requires a combination of hand gestures and mental focus.
If the mental focus doesn't align with the hand gestures, the spell won't be cast successfully either.