Suppose $S = \displaystyle\sum _ { n = 1 } ^ { \infty } a _ { n }$ is a convergent series and $a_n ≠ 0$ for any $n$. Explain why the series $T = \displaystyle\sum _ { n = 1 } ^ { \infty } \frac { 1 } { a _ { n } }$ must diverge.