There are (situations) where a group of people are gathered together because they are all (associated in) some formal way－for example, they share a (strong) interest in some hobby or sport. Now, into this group may come an "outsider"－someone that the others possibly know, but who is not a (regular )member of their in-crowd. This "outsider" is welcomed and accepted, and perhaps is even considering joining their group (officially). For now, however, that "outsider" does not "(belong)." In this situation, if anyone asks that outsider, "Why are you here?", that outsider could answer. "I just came along for the (ride)." The meaning is, "I am an (extra) person who does not really belong, but because I am accepted, I am happy to be here for now." The situation could (involve) actually riding somewhere together, as on a tour bus, or (simply being) in the same place as others.
free ride 不劳而获
to let something ride 不採取行动改变错误、不纠正错误，顺其自然
to take someone for a ride 蒙敝或欺骗他人
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