What's the deal with people who are always late?

I'd like to get to the root of the reason why some people are ALWAYS late. Consider that a time & familiar place have already been established. Also, consider that the people have a full tank of gas & a functional means of transportation. Just to give the "late-comers" the benefit of the doubt, let's also say that they didn't forget to bring something or didn't have to stop anywhere along the way. Finally, let's also say that there are NO traffic jams, accidents, detours, or other obstacles. OK, even with the ideal conditions described above, WHY are some people still always late!?