  There are two paradigmatic frameworks for treating quantum systems coupled to
a dissipative environment: the Caldeira-Leggett and the
Ambegaokar-Eckern-Sch\"on approaches. Here we recall the differences between
them, and explain the consequences when each is applied to a zero dimensional
spin (possessing an SU(2) symmetry) in a dissipative environment (a dissipative
quantum dot near or beyond the Stoner instability point).
