Are they? You're able to tell this without knowing what they are?
Let me give you an example: It is a sort of universal law that matter and energy cannot be destroyed, only changed. It is also apparent that a great many things in nature are cyclical, such as a myriad of life and death cycles in the animal kingdom, the water cycle, weather patterns, the phases of the moon, etc. So, with that information, I feel that a belief in reincarnation makes sense to me, as the "soul" (or whatever energy that drives life) cannot be destroyed, only changed, and could potentially be recycled in another lifeform (or lifeforms).