The down hill biking is more difficult than climbing. While going up you need only your strength but when going downwards you need to relax your upper body and a tight grip on your handle. You are advised to slow down and apply brake when approaching the rock or any other obstruction.
If the brakes are not applied on time the rock will stop the wheels and it is not a good idea as the rock can throw you off the bike and make you slow.
If you are relaxed you will not slow down much but you will need to give both extra momentum and no front braking to keep the wheel away from the rock and continue your journey down.
If the pace is slow then you can release the brakes when coming closer to the rock. On hills going slow will always make things difficult.
The only exception being a turn where you will need to slow down to allow the radius of turning wheel and it needs lots of practice. This will improve your balance while going downhill. The down hill biking is the most dangerous kind of mountain bike and it can be very thrilling and need lots of practice.
With a lot of practice and learning the right techniques, you will find that down hill biking is much more fun and it gives you enjoyment and excitement for those who like a little bit of adventure.