The probability that a randomly thrown dart will land on a target is $\frac{3}{8}$. What is the probability that the dart will not land on the target? Express your answer as a common fraction.
By the notion of complementary probability, if the probability of a dart landing on the target is only $\frac{3}{8}$, then the probability of it not landing there is $1 - \frac{3}{8} = \boxed{\frac{5}{8}}$.