# For a system to be causal, number of finite zeros <= number of finite poles. Why?

I read in this pdf that for a system to be causal, the number of finite zeros must be no greater than number of finite poles. Why?

I know that for a system to be causal, $h[n]=0$ for all $n<0$. Can you give an explanation how the statement maps to this? Or why the number of finite zeros are less than or equal to the number of finite poles for a system to be causal?