Actually, sometimes they can.
2,5-Dibromofluorobenzene is a benzene ring carrying two bromines and one fluorine.
At first glance, those two bromines look like two identical molecular exits.
But fluorine changes the neighborhood.
One bromine sits close to it. The other lives in a different electronic environment.
And with the right catalyst and reaction conditions, chemists can exploit that difference.
Researchers have used this molecule in site-selective Suzuki coupling: attach one aromatic group first, leave the second bromine behind, then use that remaining bromine to attach another group.
Global Chemical Database