Have you ever tried to remember someone's phone
number they just told you without writing it down?
Then someone else starts talking to
you.
...and talking
...and talking.
You forgot it didn't
you?
That's because it was in your working memory, and in order to
maintain the information you have to focus on it.
Distractions keep people from remembering things short term. Maybe it's not
someone else talking, maybe it's trying to remember numbers and letters on one page
then entering them on another.
If you want people to do something specific, don't have them do
anything else until they complete the first task. Working memory
can only hold so much.