I'm going through Statistical Inference by Casella & Berger, and on page 419, in the intro section of interval estimation there is the following example (note: most of the text was left out as it's irrelevant to my question):
Let $X_1,...,X_n$ be a random sample from a $\text{Uniform}(0, \theta)$ population, and let $Y = \max{\{X_1,...,X_n\}}$, ... Note that $\theta$ is necessarily larger than $y$.
My question is why is $\theta$ necessarily larger than $y$.