Most people adjust their mirrors so that they can see part of their own car reflected in it.
They adjust them this way so they have some reference to their car when they look out, but that also cuts out a lot of viewing area behind them, and creates blind spots. The better way to adjust your mirrors is to move them so that they are turned almost all the way out, especially on the driver's side. That will give you much more viewing area of what's on your left. The right side doesn't have to be moved out as much because that's a convex mirror that already shows more viewing area. The inside mirror is just as important and should be used in conjunction with the outside ones.