River, Bridge or something else altogether

Nearly 4 years have passed now; much water must have flown under the bridge. The writer must have changed the written then is bound to change……..but wait “much water must have flown under the bridge”…….the bridge remains the same. So here is an interesting question now, am I the bridge?? or the river that flows underneath?? and it is of value to know clearly which one of it is me as the difference is drastic. Though subject to change both the bridge and the river are the rapidity of rate of change of one (the river) makes the other look almost changeless. So who am I? Am I the river of constantly and rapidly changing experiences? Or Am I the seemingly changeless observer (bridge) that is aware of all this as it is happening? Or Is this analogy of the river and bridge too insufficient to encompass the human condition?