How user solve programming problem

One day my colleague comes in the office, and says 'can you see difference between two a4 papers'. On the first sight I noticed shorter paper. As firefox and other browsers add header and footer on printing by default, users are used scissors to cut of header and footer :)) because apparently they didn't know how to turn it off.
So for those who are making web applications, if you didn't predict something like this, you should consider it next time.
They can always blame you, they are always telling a truth, and you should start from that point.