Trajectory doesn't always mean it goes down, up and then back down again. For example, the trajectory of a plane from take off to landing. The path that an object takes as it moves through the air, that's the trajectory. Upward trajectory or downward trajectory. Imagine a line showing the movement of something, making a curved line, going up and over. It could be a line on a grap ok, so it's interesting to follow the trajectory of robin's english learning,. especially that moment when he was told he wasn't good enough to pursue his studies. And then he kind of doubled down on his English education.