$Let \, x \, be\, all\, the\, person \, in \, the \: universe$
$P\left ( x \right )=x\, is\, perfect.$
No one is perfect -:$\forall x {P\left ( x \right )}'$
Not Everyone is Perfect
$\exists x {P\left ( x \right )}'$$\Rightarrow$there Exists someone who is not perfect.