Fall

Children grow by falling and falling, to be falling down is a kind of exercise, they can fall repeatedly.
Young people are not afraid of falling, they react very fast, falling is no harm to them. Besides they do not fall.
To middle aged, if fall, a bit serious, but still they can rest on bed for a few days and can recover very quickly.
For old people, it must be careful, never fall down. A serious fall may change their life.
An improper fall will cause old people to live on bed for long time, even to death, and goodbye to his life.
Most terrible is for single old person, he or she lives alone. No one can discover quickly after falling.
Old people have to take care by himself every minute. A little neglect may take his beautiful life away.