Ugh. I've had over approx 3500 needles in my lifetime. And the dialysis ones I have are 16g.  You really do get used to it though, but man is my arm fucked up.  The only time when the pain is unbearable is when the needle hits a nerve, and the last time that happened I cried like a little bitch as it had been the third time in a row they did that. I've given birth before and I swear that hurt less than this damn nerve did.