Situation
When a user is trying to submit a form, but is not allowed to due to the fact that not all mandatory fields are filled in a user can get lost and frustrated since he cannot see which field he needs to fill in because the field just falls of his screen and he needs to scroll in the form to see it.
Suggestion
When a form cannot be submitted because of an empty mandatory field and the field is not on the screen of the user (because he needs to scroll further down the form), we should help the user by bringing the field into his screen.