thermodynamics - Why do flows gain pressure with decreasing velocity?

I know it isn't always the case, but in many conservation equations velocity and pressure of a flow are inversly related, or sometimes velocity and enthalpy. My question is, "What about slowing molecules down makes then push harder?"

I understand the math but not intuitively why a flow that is moving slower can push harder, in fact I would have guessed that a faster flow pushes harder. Specifically I am looking at nozzles and diffusers.