[Of course he meant insignificant and weak from a general immortal perspective - Sebastian certainly doesn't think like that. Well. At least he doesn't dismiss how extremely significant human struggles are to humans and the strength of their despair - no human would ever enter contracts with a demon, were it any other way.]
Empathy goes only so far, even if one might wish to understand, is it? [Not to mention not every immortal is even capable of even a hint of empathy.]