Given a Lie group $G$ over $\mathbb{C}$ and a Borel subgroup $B$. There is this famous Bruhat decomposition of the flag variety $G/B$.

How do we prove the closure relations between the cells, which are indexed by the Weyl group elements?

I was thinking about constructing a curve that connects two $T-$fixed points, using the exponential map. Let $e_{\alpha}$ be a root in the Lie algebra. How do we think about the action of $\exp(t \cdot e_{\alpha})$ on $G/B$, as $t \rightarrow \infty$?