No matter what you make or build, it's the seams that are the hardest part to get right. On a piece of clothing, a loose seam will be prone to tear; make it too tight and it will restrict movement. On a house, that loose board will cause the roof to leak, and if there isn't enough room for expansion, stuff will start to buckle.
As it turns out, the body has numerous seams that need to be made just right so that they don't pull apart and let body parts slide into places they don't belong. The abdomen is surrounded by numerous muscles to keep the stomach, small intestine, and colon where they belong, but if one of these organs starts to slip though a weakness or a hole in the muscles, it's called a hernia.