The physical state of water is determined and affected by two things. At room temperature, water is a liquid, but as the temperature drops to 32 degrees it freezes. On the opposite end, water boils into steam at 212 degrees. But this is only true at sea level. Above sea level, where the atmospheric pressure is reduced, water boils at lower temperatures and freezes at higher temperatures.
Water is unstable because it is affected by temperature and pressure.
But water is also considered unstable because its molecules are not held in a rigid pattern, therefore the water takes the shape of whatever container holds it. And like the atmospheric pressure's affect on water, Reuben did not hold true to his form whenever the pressures of life pressed in on him. And like water's molecules that are not held in a rigid pattern, Reuben behaved differently with each and every situation he found himself. It is so easy to blame others when the problem is with us. If only the temperature didn't change.