For example, if you look at NASA's nice picture on engine pressures (thanks Bernd on the BA038 thread) you'll see there are different pressures on either side of the bits that go round and round and where there are different pressures the thingie in between those different pressures gets pushed.
Simple ... but the things that get pushed are not all in the forward direction and that's why most folks only talk about the exhaust when in fact it's the summation of the forward and the aft pushies
