Happens all the time on inland waterways. Your boat will be pointing at the next can but you're crabbing off into 2 feet of water still pointing at the mark.

I had a boat behind me and was watching his slide out of the channel but pointing at my stern. He still thought he was doing fine. I hailed him and suggested he look behind him. He did, realized he was out of the channel, said a couple of explitives and about 2 seconds later ran aground. He managed to get free but it happens all the time, not going the direction your pointing.

Don't need a GPS for that though, you just have to look behind you once in a while.

A major one for me was heading east from Venezuelas Testigos. About 4 hours out my compass said I was headed 80 deg., the GPS said 350. That's major.