When a sighted user fills out a form, they go through the process of filling in a field, tabbing over to the next field and filling it out until the form is completed. This is easy for visual users since the labels are placed in a way that they seem to be linked to each of the fields. For someone who is blind and/or using a screen reader, the visual layout will not be helpful and though they can see each of the input fields, they might not know what label is associated with that field.