There are those types of things that are conflicting, and the way that we typically view Sunday is one of those conflicting things, because the calendars that we have, whether printed, online, or on our phone, consistently show that Sunday is the first day of the week. Yet, somewhat puzzling, everyone agrees that the weekend consists of Saturday and Sunday. So there appears to be a real conflict between what Sunday actually represents -- for it does not appear possible that it can simultaneously be the first day of the week as well as representing the last day of the week, which is thereby best answered by looking at history.
When it comes to the Judeo-Christian religion, we find that those of the Christian faith believe that Sunday is the first day of the week, because Sunday was the day that Christ arose, and therefore Sunday represents the resurrection of Christ, and thus the new beginning of humankind. In regard to Judaism, their sabbath begins at sundown on Friday and ends about an hour after sunset on Saturday, which thus means that Sunday represents the first day of the week for those of the Jewish faith.
When it comes to those that labor for a living it is important to recognize that the traditional forty hour workweek, which typically is from Monday to Friday, has only been the norm for a relatively brief period of time, of about one hundred years, in which, previously the standard workweek including working on Saturday, so that Sunday was thereby seen as a day of rest, recovery and worship, which basically signified that the week effectively ended upon the end of the workweek, and thus the new week began on Sunday.
Nowadays, since the forty hour workweek of five days is the standard in America, of which the business world partakes of a Monday through Friday schedule, this signifies that Saturday is no longer a workday, and because Sunday never was a workday, this would seem to suggest that the combination of Saturday and Sunday as non-workdays thus represents the weekend, which logically makes sense, but nevertheless the calendar still shows Sunday as the first day of the week, which probably is an accommodation to the importance of religion and the tradition of religious faith in our lives, and also as a reminder to us, that life shouldn’t necessarily be in conformance to what the workweek represents, but rather should be in conformance to that which is beyond work.
So then, we find that in all probability the way that our calendar is presented is not going to change anytime soon, and further to the point, most people probably don’t pay any real attention to the fact that the week appears to begin on Sunday, because it isn’t something that changes the fact that for most people the weekend is represented by Saturday and Sunday, and what tradition dictates about the beginning day of the week they pay no real mind to.