Sven and Ole are up fixing the roof. Sven picks up a nail, looks at it, and throws it away.
He picks up the next one, looks at it, and hammers it into the roof
The next one, he hammers it into the roof; the next one, he throws it away.
Ole says, "Sven, why do you throw away half the nails?"
Sven says, "Ole, don't you see, they have the point on the wrong end!"
Ole says, “Sven, don't be such a dummy! Those are for the OTHER side of the roof!”