Monolinguals consistently underestimate how hard it is to reach proficiency in another language. The exception to this being being raised in a multilingual home

Monolinguals consistently underestimate how hard it is to reach proficiency in another language. The exception to this being being raised in a multilingual home. I don't know what their reasoning is. They can plainly see around them foreigners struggling to speak, but they somehow think that it won't happen to them?