I'm answering the literal and metaphorical question.
Say you have two rivers that are parallel and symmetrical, any little disturbance or alteration to the direction of one of will gradually make them end up in very different locations (may take years, but will happen 100%). Also, the geography of the land probably will not be the same, further making the destination of the two rivers very distant.
Now imagine two friends that have grown up in a married, middle class, family, they have went to the same school, had similar career goals, and hang out with the same friends. Friend one plans to be a nurse and the other a veterinarian. They start out the same, but as the education there're career(s) require, the farther they end up. Life is unpredictable and NOTHING is ever guaranteed.
Hope this enlightens people, this is my first answer.
