The word 赶上 is formed through a vivid metaphorical combination: the first character 赶 carries the core idea of "rushing" or "chasing after", implying urgent motion, while the second character 上 means "to go up" or "to board", indicating successful contact or attachment. Together, they create a single concept of "catching up to and getting onto" something that is in motion or progressing, like a bus, a trend, or a point in time, perfectly capturing the moment of successful connection after pursuit.