Today we were learning about atomic structure, our teacher introduced the mathematics of the 'Niels Bohr Model of Atom', and calculated the value of total energy $\frac{-13.6z^2}{n^2} \pu{eV}$. He explained that when the value of $n$ tends to infinity, the value of total energy tends to $0$. Mathematically I understood this.

I couldn't understand, or comprehend, how or why the energy of an electron can't exceed $\pu{0 eV}$? What is the reasoning behind it; why is it not possible and what is the physical significance of it.

For the sake of the argument, what would it look like if the total energy of an electron were to exceed $\pu{0 eV}$?