True...
What I actually meant was that I've found on a few occasions the forecast wind - and my related calculations - have not resulted in correct timings over waypoints. As a result I have had to modify my ETAs in the air a few times. My calculations were correct as per the forecast wind, so the actual wind must have been different.
GPS will help me work out whether the forecast wind and actual wind are similar by reference to my expected ground speed and actual groundspeed. This will allow me to make minor corrections without the need to get lost, if I'm not mistaken?