Sure. As is said upthread, GPS isn't pefectly accurate. Remember, the little circle around your position isn't really accuracy, it's confidence. "I'm pretty sure you're in this circle, probably around the middle."
Sometimes a whole GPS session can be off - it looks like it's slipped North 10m, say. Most of the time, after a couple of hours of operation, it's very repeatable and that's as good as we can hope to get. The device is very confident of its silly position.
When there's only one trace, unless you've got other cues to tell you that it's off (like known junctions all being shifted the same way), you've got to treat the GPS trace as authoritative: It's the only data you have. Apply a brain-based smoothing algorithm ("that bit was straight really") and cartographic elegance and you're winning.
When I'm mapping a burb, I like to walk / ride the main roads a couple of times. It usually happens by default just through "getting" everything, and it makes it easier to see where the real centre of a junction is, or the real shape of a curve.