  The occurrence of mesoscopic fluctuations in statistical systems implies,
from the point of view of dynamical theory, the existence of local
instabilities. However, the presence of such fluctuations can make a system, as
a whole, more stable from the thermodynamic point of view. Thus, in many cases,
a local dynamic instability is a requisite for the global thermodynamic
stability. This idea is illustrated by several spin models.
