My first was very hard to breastfeed because I didn't produce enough milk for one reason or another and was only able to breastfeed for three months. (babycenter.com)
I did not produce enough milk for him and experienced major anxiety over it, which made it worse. (yummymummyclub.ca)
It is true that some women don't respond well to the pump and do struggle with producing enough milk when they are using one, but this isn't the case for everyone. (exclusivepumping.com)