Because the brain actively and continuously re-engineers itself, merely thinking about something changes the brain itself. So if we know how that works, the very knowledge of how the brain functions then changes the way the brain functions.
It’s a tight loop, but it also has effects on a social level too. Like the important scientific discoveries and perspectives that have changed peoples mindsets, for example the understanding of the term ‘ego’ and the relativism revolutions, this understanding of neurons will also feed back into the way the brain is structured, in a larger loop. Not only do we know different things, we now think differently, maybe so much so, that an intellectual discussion between a contemporary citizen and one from say, two thousand years ago, would be nigh-on impossible. Thus social events feed back in very real and tangibly physical ways in terms of how our brains are structured.