They were told in advance how hard it can be at the beginning.
All you hear is how good it is for baby and all the health benefits for mom too.
No one mentions the awful pain from baby learning to latch (two weeks' worth at least for many women), or the frustration of a big baby being fussy and hungry for days until your milk comes in.
My son was almost 11 lbs, and when I broke down and gave him formula after he couldn't get full from nursing, he ate two full ounces on several occasions. I know the colostrum is sufficient for nutrition, but not for filling an empty tummy. (He's now content with nursing and only gets formula when I'm too sore to handle it).
It's just discouraging to be trying to do the best for your baby and dealing with something like compression injuries (after ONE nursing session) that the LC doesn't know how to fix, and to think "I don't know how long I can do this" instead of "It hurts everyone for a few weeks - I can handle that."