system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why when you turn on a hose, you have to wait a while for the water to reach the end, but increasing the pressure afterwards causes the output flow to rise almost immediately?
gpt
Think of the water like some marbles in a tube. 

If the tube is empty and you add a marble, it has to travel all the way down the tube before you see the same marble come out the other end, which takes time. 

If the tube is already full of marbles and you force one marble in the end, then each marble pushes the marble in front of it and a different marble pops out the other end almost instantly. The marble you added didn't travel super fast, it's still in the tube, it was a different marble that got pushed out.