How about this analogy -
You take your sand yacht out on a day when the wind is blowing 10 knots over the land, from east to west. Since your sand yacht can go downwind with a VMG greater than the wind speed (see
https://en.wikipedia.org/wiki/High-performance_sailing), you can sail yourself west with a VMG of, say, 20 knots. So you're going along in a north-westerly direction, moving west at 20 knots and north at, say, 10 knots. Still good?
Now, you look out toward the horizon and you see a body of water. The water is moving relative to the land from east to west at 10 knots. Therefore, the wind is not moving over the water. You're going west at 20 knots, so relative to some point on the water you're going west at 10 knots. Still good?
Ok, now, in the paragraphs above, do a copy/replace. Replace every instance of "sand yacht" with "foiling catamaran", every instance of "water" with "ground", and every instance of "land" with water. Those find/replaces don't change the physics of the situation in any meaningful way. What do those paragraphs say now?
Here's what it says. I promise, all I did were those 3 find/replaces.
You take your foiling catamaran out on a day when the wind is blowing 10 knots over the water, from east to west. Since your foiling catamaran can go downwind with a VMG greater than the wind speed (see
https://en.wikipedia.org/wiki/High-performance_sailing), you can sail yourself west with a VMG of, say, 20 knots. So you're going along in a north-westerly direction, moving west at 20 knots and north at, say, 10 knots. Still good?
Now, you look out toward the horizon and you see a body of ground. The ground is moving relative to the water from east to west at 10 knots. Therefore, the wind is not moving over the ground. You're going west at 20 knots, so relative to some point on the ground you're going west at 10 knots.
Those last 2 paragraphs are you, sailing upstream through a current, with no air blowing over the land.