It’s easy to feel a bit down if right before you start your hike, it starts to rain. This is especially true for people who have never hiked in rain, or people who do all they can to avoid it.
Embrace it. Rain is yet another side of the mountain you get to see. It also feels really great once you’re off the mountain after going through some rough patches.
(If you’re not prepared for wet weather, or if there is a risk of landslides, thunder, and the like, don’t go on the mountain or get down as soon as is safe. Never ever underestimate a mountain!)