I haaate when people say this. It's right up there with we can't all be perfect.
Seriously, people who say this sound like whiny teenagers with bruised egos.
It doesn't help that it often follows the admission of doing something stupid/dangerous/ill-advised with their babies. Like, I let my 10 month old watch Frozen ten times back to back. I guess I'm just a bad mom. Uh, yeah. Barring extreme circumstances, you kinda are. But even if whatever it is you're "admitting" to is something totally normal, that in no way makes you a bad parent, the sullen-stompy footing discredits you hugely.
Anyway, that's my little rant for the day. The monster is teething and fussy, but otherwise wonderful, and I'm calling 1st thing Monday to set up a therapy appointment. More to follow on the cuteness of a singing 10.5 month old.