  The Pauli exclusion principle plays an important role in many-body fermion
systems preventing them from collapsing by repulsion. For example, the Pauli
principle causes a repulsive potential at short distances between two $\alpha$
particles. On the other hand, the existence of nuclear rainbows demonstrates
that the inter-nuclear potential is sufficiently attractive in the internal
region to cause refraction. The two concepts of repulsion and attraction are
seemingly irreconcilable. Contrary to traditional understanding, it is shown
that the Pauli principle causes a {\it universal structural Pauli attraction}
between nuclei rather than a {\it structural repulsive core}. Through
systematic studies of $\alpha$+$\alpha$, $\alpha$+$^{16}$O, $\alpha$+$^{40}$Ca
and $^{16}$O+$^{16}$O systems, it is shown that the emergence of cluster
structures near the threshold energy at low energies and nuclear rainbows at
high energies is a direct consequence of the Pauli principle.
