Yabbut.... you don't actually have to remember to breathe do you? Since it is a vital process for the body the brain has systems in place to make it always happens. It isn't really optional.
Any parent here have a toddler who used the not-breathing-till-I-get-my-way trick? I didn't but I can imagine it looks pretty scary. However the minute they black out due to lack of oxygen the automatic processes kick in and they start breathing again.