Pride
"Wow, Gramps… I thought that you were smarter than that," Rain said while blinking in disbelief. "I understand why you would underestimate me since you know my strength, but I didn't think that you would underestimate the enemies that you don't know."
"... What do you mean by that?" Seadrei asked after he raised his left eyebrow.
"What I mean is the fact that your sense of danger is severely lacking for not having to fight seriously in who knows how long," Rain said. "Didn't you forget the fact that a mere human controlled you years ago? Maybe I picked the wrong time to bring this conversation since you are too elated about the feeling of power that you are feeling right now. Perhaps Rejuvenation also brought back some of the carelessness of your youth."
"I admit that I feel like I am a hundred years younger, but that doesn't mean that I forgot my experience of five hundred years," Seadrei said.