2 added 14 characters in body

I don't think I've seen it in here:

Every vector space has a non-trivial dual space ($L^p$ for $0 < p < 1$ was a counter-example only mentioned during one of the classes in measure theory)

And of course there's the common false belief of people outside of mathematics that "mathematicians work with numbers and formulae all day long" :)

Every vector space has a dual space ($L^p$ for $0 < p < 1$ was a counter-example only mentioned during one of the classes in measure theory)