For a person to walk on any surface, he/she must experience friction force. The friction of the surface allows the person to walk on it without slipping. Since, solid ice is very smooth and it does not provide any friction between its surface and any other material, it is not easy to walk on it. During the walk, the person applies force on the solid ice surface which is greater than the friction force of the ice. Hence, the person slips and cannot walk properly.