Everybody must avoid day dreaming, but this is especially necessary for workmen in factories. there are fours common kinds of day dreams which make workers careless and inattentive.
The first is emotional day dreaming, like letting the mind dwell continually on the thrills of some strong emotion like love. a second is characterized by worry about imagined misfortunes, most of which never happen.
Third is the kind of day dreaming due to retrospection; looking back on the pleasures or missed opportunities of the past. last on the list are the day dreams of vengeance, in which the victim goes over and over again in his mind the terrible things that he will do some day to some enemy or antagonist.
Source : Interpretation of Dreams by Sigmund Freud