No injection feels the same, sometimes it's so smooth and painless you feel like you can do it 100times. Next day the needle hurts like hell just getting through skin, then it's ok, you push the needle deep then 5mm from fully in you go through a vein, or scar tissue and it feels like a bee just stung you.
The worst is when you've rotated injection sites but come the day to inject site 1 it's still sore from the last time especially if 2ml was injected in one go. Then you know this one is going to be a painful one. I'd say every 1 in 5 hurts much more than the others.