I oftentimes wonder why my parents were always hard on me whenever I got anything less than a B when my sister frequently failed. In my case, i'm the youngest child, so i'm sure it's not just what order you were born in. Particularly if you are getting good grades frequently, a parent is more scared that you are losing your edge, while it's impossible for another child to fall further, they are not as concerned about it.
Also, technically in college anything lower than a C is a failing grade anyway. That is to say, most colleges cut their majors off at 2.5, which is between a B- and a C+. They drop students when below 2.0, which is a straight C.

