Question about the binomial coefficent why is ${1} \choose {i-1}$ $=0$ if and only if $i-1>1$?

Question

I've come across a statement that says we have ${1} \choose {i-1}$$=0$ if and only if $i-1>1$. I don't know how to interpret the binomial coefficient when the bottom term is greater than the top. Why does this hold?