  The collective structure of $^{106}$Cd is elucidated by multi-step Coulomb
excitation of a 3.849 MeV/$A$ beam of $^{106}$Cd on a 1.1 mg/cm$^2$ $^{208}$Pb
target using GRETINA-CHICO2 at ATLAS. Fourteen $E2$ matrix elements were
obtained. The nucleus $^{106}$Cd is a prime example of emergent collectivity
that possesses a simple structure: it is free of complexity caused by shape
coexistence and has a small, but collectively active number of valence
nucleons. This work follows in a long and currently active quest to answer the
fundamental question of the origin of nuclear collectivity and deformation,
notably in the cadmium isotopes. The results are discussed in terms of
phenomenological models, the shell model, and Kumar-Cline sums of $E2$ matrix
elements. The ${\langle 0_2^+ ||E2||2_1^+ \rangle}$ matrix element is
determined for the first time, providing a total, converged measure of the
electric quadrupole strength, $\langle Q^2 \rangle$, of the first-excited
$2_1^+$ level relative to the $0_1^+$ ground state, which does not show an
increase as expected of harmonic and anharmonic vibrations. Strong evidence for
triaxial shapes in weakly collective nuclei is indicated; collective vibrations
are excluded. This is contrary to the only other cadmium result of this kind in
$^{114}$Cd by C. Fahlander et al., Nucl. Phys. A485, 327 (1988), which is
complicated by low-lying shape coexistence near midshell.
