Humans have the innate magical power of walking on two legs, but it can take several years to master it. However, as the legs are an external organ, it's obvious what could be done with them. If they were internal organs, such as the aforementioned dragon 'ice lung', and nobody knew they were there, or had ever used them accidentally, or ever autopsied another human, it could possibly lead to the ability never being learned. It is extremely unlikely and implausible in real life, but plausible in fantasy. Of course, considering breathing is a reflex and not a learned ability, it makes no sense.
Did anyone ever forget how to breathe?