It is important. But there are many way to learn and get good at it.
I find the young dentists that I work with that have poor hand skills get better with time and practice.
I also find the young dentists that come to me with good hand skill tend to have had life experiences that helped develop those skills. Examples would include sewing, model building, carpentry, electronic gadget repair, origami, auto body work , puppetry, welding, cake decorating, sculpture, slight of hand magic, bicycle maintaince, etc.