The first is the distinction between the stability of a system and its volatility. This is best done visually.
In the bowl at right, if the ball is dropped, or the bowl is wobbled, the ball will move. There will be volatility. However, the system is inherently stable. The ball will always have a tendency to move towards the bottom of the cup.
Conversely, the system represented by the bottom bowl is unstable. The starting point for the ball may be stationary, with no volatility. However, the slightest wobble will see the ball move. Furthermore, the end position of the ball cannot be predicted. Minute changes in its starting point or the direction of the wobble will result in very different outcomes.