Imagine that you live outside of the city limits, and therefore instead of the public sewage system, you have a cesspool in your backyard.

Now, imagine that the cesspool is leaking (you notice because the patch of long, dark green, healthy looking grass). It's leaking into the stream where you get your drinking water from, so obviously it's pretty important to deal with the matter.

So, you dig down to the cesspool, which you discover to be something your great-grandfather built in nineteen-hundred-and-ought-three out of bricks, and obviously won't do. But digging a new cesspool is a lot of work, you think; maybe I can just patch this one. So you take the mortar tray down into the hole, looking for the leak. Problem is, the walls are completely covered in shit, so you can't tell where the leak is coming from.

So you make an educated guess that the side closest to the stream is where it's bad, and try to patch it. Problem is, mortar doesn't stick to shit, so you have to clean all the shit off that part of the wall first. No problem, get a rag, wipe it clean - no, this is a brick wall. All the mortar has fallen out, leaving deep holes between the bricks that have filled with shit. That shit will have to be removed - via pipe cleaners, toothbrushes and the odd paperclip, so that the new mortar can be added.

So you spend two days cleaning that part of the wall, reapplying the mortar, letting it dry... and the leak is still there. Somehow you track the leak to some unlikely corner on the OPPOSITE side of the cesspool, clean the shit out of it (more difficult in a corner), apply the new mortar, let it dry, problem is fixed - BUT WAIT! All that cleaning and fixing and wiggling things has loosened the bricks closest to your house and now the cesspool has a NEW leak - straight into your basement!

At this point you sell the house.