Provide an example of a Banach space $X$ and a functional $f$ in $X'$ such that there is no unit norm vector $x$ in $X$ satisfying $|f|=f(x)$

Question

Give an example of a Banach space $X$ and a functional $f$ in $X'$ such that there is no unit norm vector $x$ in $X$ satisfying $|f|=f(x)$.