Why can't we meet all of our protein needs in one meal?

Because most people go for what tastes good rather than what is protein rich, and what tastes good is usually high in fat and carbohydrates, as opposed to proteins.

geologic time scale (for gradpoint) =)

sorry to break it to ya but no one can answer your question it's just

jk but i am serious about the part that most people cant answer it beacuse you did not mention the section you are talking about. but it would if you added some detail and were a bit more specific.