**Abstract: **
The talk presents a case study that illustrates that different
boundary conditions can cause remarkably different physical behaviour
for otherwise identical quantum mechanical systems. We consider a one
dimensional well with Dirichlet boundaries that is separated into two
halves by a thin nonpermeable wall. The two half wells are populated
by the same number of identical noninteracting particles of the same
type, kept at the same temperature. The only difference is the
reflecting boundary condition at the inserted separating wall, which
is Dirichlet from one side and Neumann from the other side. We
calculate the quantum statistical pressure on the two sides and find
that their difference - the net force acting on the separating wall
- is nonzero and asymptotically diverges with increasing
temperature.