What makes your analogy even more intruguing is that there is also the possibility of someone coming along and reaching into your little rock pool and moving things about, taking things out, and even putting things in.

I like that, since it's indicative of the effect those around us can have on who we are - I know some people say only we can change ourselves, but I'm not entirely sure that's the case. At least, maybe some of our changes are done subconsciously, in response to those around us - it's not something we make a conscious decision to do, but rather something that just happens (for good or ill).