Imagine that you’re filling your bathtub for a nice relaxing soak. You’ve got the water on full blast at just the right temperature, and the soap suds are perfectly proportioned. Yet there’s a problem: the water rises to a decent level, but never quite tops out to where you’d like it. Despite leaving the water on and stepping away for a while, nothing changes.
Then you realize the source of the problem: there’s a hole in the drain. It may just be a small one, but it’s a hole—water disappears down it in one direction only, never to return.
What do you do? You could leave the water on full blast for the entire soak, which might not be that relaxing. Or you could try to fix the problem by plugging the hole.