  We investigate the exotic hadrons consisting of two light quarks and two
heavy antiquarks, $(q\bar Q)$-$(q\bar Q)$. The spin-dependent term between
quarks is known to give an attraction to the $ud$ spin-0 component in the
isospin-0 $u\bar c d\bar c$ system, $T_{cc}$. However, the said component also
gets a repulsion from the partial Pauli-blocking. By the dynamical calculation
with a simplified quark model, we discuss that the competition of the two
effects leads to a shallow bound state for $T_{cc}$, which is preferred from
the experiment, and a deep bound state for $T_{bb}$.
