If you tighten it too much you will warp the Oil pan its self! When you crank on the drain plug like hulk would.... you end up twisting the actual threaded piece that is welded to the inside of the pan. This distorts the outside of the pan and thus.... a leak that will never stop. There are only 3 small spot welds that hold the threaded part to the inside of the pan, its very easy to twist it and distort the sealing area just enough to cause a leak.
Picture of what happens when people over tighten or try to reuse the crush washer and it leaks so they tighten it more.