Imagine you have a placeholder in a date field that tells you the format in which you should enter the date ("mm/dd/yyyy"). You enter the date and that informat

Imagine you have a placeholder in a date field that tells you the format in which you should enter the date ("mm/dd/yyyy"). You enter the date and that information is no longer visible. You finish the form and think "Wait a second, was that supposed to be mm/dd/yyyy or mm/dd/yy?". That's the general idea.