[tongzilla]

When you see a curved line, does that mean you physically try to putt the ball in a curved line? I don't think so. Instead, you still make a STRAIGHT PUTT, but the slope is what causes the ball to curve.

For those curved liners out there, whether you realise it or not, you have automatically seen the straight line once you have visualised the curved path of the ball. The straight line is simply the starting direction of the curved path.
Vice versa for straight liners. You cannot know where to point your straight line unless you can visualise how the ball is going to curve into the hole. By seeing one you see the other.