Why $\mathbb{P}(\max\limits_{0 \le t \le 1} B(t) > \epsilon n) = 2\mathbb{P}(B(1) > \epsilon n)$, $B(t)$ is a Brownian motion

Question

When I try to read the proof of Law of Large Numbers, there is a step as the tittle of the question, I would like to know why it works. Thanks beforehand.