This is one reason I hate Scrum. Companies that (I've worked for) have really tried to implement it don't understand that sometimes you just won't be as productive. It's always, "Well you committed to it...." They can't (or don't want to) understand those miracles they want their employees to perform comes at a cost. It means those people are less productive at times while they are exploring an idea or they are just exhausted. If they just want someone to do the minimum set each sprint, that's fine, just don't expect anyone to walk on water when you need to be saved.