Why is it that some people get results with dermarolling and some don't?

Some people swear by it and others say it did nothing or even made their skin worse!

I've been reading up on it and there are so many conflicting methods and products to use so its hard to know what is the official correct way to go about it.

Are there any definite situations that would see the dermaroller be INEFFECTIVE?

And is there anything you MUST do to see results?

Because they use .5m/1m. Roll/Needle lightly =/= no bleeding.

They swear by it because they probably got professional needling done or needled themselves correctly and never missed a treatment (4-6 weeks apart)

Are there any definite situations that would see the dermaroller be INEFFECTIVE? Different types of scarring

And is there anything you MUST do to see results? Consistency, the right topicals, diet and hope. And taking pictures. I'll be posting my blog up soon