Because the center of gravity on the mountain is downward, its own force is upward, and the two forces are in opposite directions and in a state of balance, except for a little exertion, the danger is small; Going down the mountain is different. It is difficult to grasp the balance because the center of gravity is down and the force on itself is down. If it is not good and the forward momentum is too great, danger will occur. And if you go downhill too fast, your legs and feet will tremble with acid.

In addition, when going down the mountain, the lower limbs have to bear several times the weight of the human body, and too much pressure on the knee joint will cause damage. It won't be like this up the mountain.

There are also metaphors for not doing wrong.

Once you make a mistake, it's hard to go back.