What's the Point of the Pleural Cavity?

The pleural cavity is one negative so that both membranes are sucking together towards each other. But there's a fluid there keeping it stuck as well. By expanding your thoracic cavity, you expand your lungs. Decreasing the pressure in your lungs, air gets sucked in. And this is just fairly passive inspiration. So it's not cool. A wide breathing. It's not forceful. It's just like we're breathing now at rest. Well I get very excited. So I'm probably doing a force. A bit of force. Okay. You who's always cool, calm and collected regardless of what I say or do,. Always doing that quiet breath of around about half a liter