Lines that are straight in real life appear broken in a stitched image on Panorama. Why?

Broken lines are caused by a phenomenon called parallax. As you move the camera the point of view change. You get a similar effect if you close one eye at a time and look at the same object; it will appear different because the point of view changes. The problem is more likely to arise when objects are very close to you. In general it is not easy to stitch objects from different points of view. Please see the tips for making Panoramas work well to alleviate this problem.