bookworm
A GoTo in your GPS gives bearing, distance and a track line from your
current position to the waypoint. Your current position is moving, therefore this track line will also move around your destination as a result of you deviating from the desired track.
Imagine the wind is from the South and you stick a GoTo in your GPS to a waypoint 20 nm East of your current position. You set off heading 270. As you fly along the wind drifts you North. Your GPS will still be giving you bearing and distance but the bearing will have changed to something less than 270 as your destination is now further South relative to where you now are.
The GPS will be showing the track from your current position to your destination, not the track from where you started, as it would if you had set a Route rather than a GoTo. Your resulting track over the ground will be a curve, drifting to the North of a straight line between your start point and destination with your heading gradually turning more South to correct for the drift.
Of course you could try flying so that the bearing to your destination remains constant as CSX001 suggests but this requires you to establish a suitable offset to your heading, which usually involves deviating from the direct track while you work out how much offset is necessary.
It's similar to the problem trying to home on an NDB by simply pointing at it.
2D
Not an aviation GPS but the map display on my Garmin 12XL can be set to
DTK Up (Desired Track Up)
Track Up
North Up
My Magellan 315 offers
Course Up (equivalent to Desired Track Up)
Track Up
North Up
I was using "Desired Track" to indicate the track you wished to fly and "Track" to indicate the track you actually flew. For some unaccountable reason these always appear different on my GPS
Mike
PS
I am assuming here that we are talking about a straightforward GPS without a heading input and therefore not capable of calculating wind drift and presenting a course to steer.