Question

why is the one end of drawing pin kept wide, but the other end very sharp ?

Answer 1

Pressure is inversely proportional to area. So, smaller area will exert more pressure, hence in a drawing pin one side is made sharp so that it can easily go inside a board and the other side is made pointed so that it doesn't exert too much force on our hand

Answer 2

so that it cannot Pierce through our thumb and second and is sharp so that it Pierce through the paper.