Let $\mathfrak{g}$ be a finite-dimensional semisimple Lie algebra over an algebraically closed field $k$ of characteristic $0$. Let $\mathfrak{h} \subset \mathfrak{g}$ be a Cartan subalgebra, and let $\Phi \subset \mathfrak{h}^*$ be the corresponding root system. If $\alpha \in \Phi$, then $2\alpha \notin \Phi$.