I don't know you, but when I know exactly (or even approximately) how difficult something is I say "It's [really] not that hard". Someone saying "how hard can

I don't know you, but when I know exactly (or even approximately) how difficult something is I say "It's [really] not that hard". Someone saying "how hard can it be" is kind of a flag that they have zero idea of how hard it is or isn't.