Do you remember how in the cartoons that we watched when we were young a precariously balanced character can be made to fall by the most insubstantial of things--like a feather or another character's breath? Or how a single drop of standard NaOH could make a clear phenolphthalein laced analyte magenta (sorry for the Chem analogy)?
I suppose it's true that, often, the most mundane of things can cause a turn of events that completely changes a situation. A careless comment can make a person lose hope completely and a thoughtless action can make a person realize how dispensable and replaceable he really is.
The very things we take for granted, much like the weight of a feather, can make all the difference and cause something to tip over to a point of no return.