Recently I had been to a doctor. He gave me an injection on my upper arm. I used to be very afraid of injections. But the way he held my arm and pierced a thick long needle in my delicate upper arm changed it all. Now, I would love that pain of prick. Why did I started liking injections?

Maybe you grew up. With up to 7 injections/day and 4 pricks/day of the finger, they don't hurt in the least. Neither does accupuncture, which feels a lot better.