>>11156234If you actually did the experiment you would immediately recognize the error.
Actually take a physical sheet of paper. Blow from the longer side when held as on the gif. The page either doesn't move at all or is pushed _away_ from the air if you don't do this perfectly perpendicular.
Now fold it at (longer) end so that the fold is on the opposite side from the one you are blowing on. Not very hard, make it a curve of about 60 degrees. Now when you blow the side with the fold is going to _into_ the air stream, because the air is curved by the fold and redirected in the opposite direction.
The air has to be redirected, it can be done by using the viscous forces (more efficient) or by simple direct impact over a flat surface at an angle, but the principle is the same as in a rocket.
