How far back do we really need to floss?

As in, our teeth, how many teeth back do we really need to floss? Like ok, you know the two front teeth on the top tow, pick one and count back 5 teeth including the one you started counting from, that’s how far back I floss. So my question is, do we really need to floss the teeth back there? That is a true pain.

And also, do we really need to floss in the morning as well? Because isn’t flossing to get rid of food in between teeth? What food would be in between teeth in the morning? It’s already all flossed out from the previous night..