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."