When we start designing something, we sketch out ideas with a big, thick Sharpie marker, instead of a ballpoint pen. Why? Pen points are too fine. They're too high-resolution. They encourage you to worry about things that you shouldn't worry about yet, like perfecting the shading or whether to use a dotted or dashed line. You end up focusing on things that should still be out of focus.— REWORK, 37signals.com