Trees are the cars of mountain biking, but if one collides with you, it's harder to get your buddies to back you up that it wasn't your fault.
BONUS TIP: squirrels are the pedestrians of mountain biking - constantly emerging from nowhere and risking their skinny mammalian necks. Big jumps are the police cars of the forest - audacious riding will be punished and meekness rewarded. Swallow your pride, rookie. Dismount and walk past, if you have to.