1. The head of a drawing pin is flattened and the other end is pointed.
2. When enough force is applied to the head of the pin, the pressure due to the force on the pointed end increases tremendously and the pin can be easily inserted in the drawing board.
3. When we press the flattened end, the force applied spreads over a larger area. This reduces the pressure of the reaction force acting on the thumb. Hence, the thumb is not injured.
4. If the head of the pin is sharp, then the pressure due to the force would be more and hence the pressure of the reaction force would also be more and the sharp end would prick the thumb causing injury.