When you sew two pieces of fabric together, the line you are sewing is the seam. Coal appears in long, linear underground deposits referred to as seams.
A garment that is coming to pieces will often first tear at the seams, the weakest parts. People use this image to describe anything that has reached a point where it is simply not holding together––your car could be falling apart at the seams, or if there's been a lot of stress in your life, you could be too — and you might have to move into a seamy neighborhood.
