The exhaust manifold flange where it attaches to the cylinder can be warped. This can and will cause premature gasket failure. When you have the pipe off lay a sheet of medium grit sandpaper on a known flat surface and rub the flange across the paper. You'll be able to see immediately if the flange is flat or has a warp to it. Most of the warpage I've seen is not bad enough that you can't sand it flat with a little time and elbow grease. The machined surface of the cylinder is usually pretty good but you can check it with the same method only use a flat file and sand cloth or paper to see if there are high or low spots that need attention. A good mating surface, a quality gasket and proper torquing of the fasteners will assure maximum life for the exhaust manifold gasket.
And no, you're not an idiot. An idiot wouldn't have asked for help.
Tom