\[- \left( - \frac{2}{3} \right)^{3} = \frac{2^{3}}{3^{3}} = \frac{2^{2} \cdot 2}{3^{2} \cdot 3} =\]
\[= \frac{4 \cdot 2}{9 \cdot 3} = \frac{8}{27}.\]