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A bootstrap sample of size $n$ is drawn by sampling with replacement from the $n$ observed data slots. Some observations occur repeatedly. For a given slot, every draw misses it with probability $1-1/n$, so its omission probability after $n$ independent draws isBy linearity of expectation, the expected number of omitted slots is $n(1-1/n{)}^n$, whether or not their omission events are independent. For the three-observation exact bootstrap distribution for three observations, an individual slot is omitted with probability $8/27$ and the expected number of omitted slots is $8/9$. This finite-sample calculation explains both repeated values and incomplete coverage; $e^{-1}$ is a limiting expected proportion, not an exact fraction in every resample.