why did needles should have pointed tips
Needle are meant for piercing things. So, the pointed tips allows the needle to exert high pressure on the surface to be pierced.
Pressure = Force/Area
So, for small surface area, ie. For pointed tips small force can produce large pressure.
Thus, pointed tips of needle help piercing surfaces easy.
when needles have pointed tips, they are able to peice easily into any soft substance. this is because the force applied on the needle gets concentrated at a single point. thus the needle is able ti pierce easily. but when the tip of the needle is blunt, the force applied gets distributed amongst the blunt edge of the needle and thus the needle is not able to pierce. therefore needles must have pointed tips.