Yesterday is important because tomorrow is shaped with our past. However, I think if we focus on present, we can make a great past and tomorrow together. 

I am more worried about the day before yesterday :)

   Worry is not an effective   address of any human difficulty and that is why it has never been objectively advocated as a means of address of human difficulties.

     It has been suggested that we adopt prayer, and that is the  coping mechanism that I have adopted  to deal with my difficulties.

Why would someone worry about yesterday? It's already known! Everyone worries about the future, because it's mysterious. Even if you don't think about it and know that worrying is useless, sometimes you'll just find yourself worried! So don't worry about worrying :D 

Personally I worry a lot about my future. In a small dose I suppose worrying could help productivity but in a great amount, no... I wouldn't recommend it.

I agree with you in that I don't think we should worry about the past, present or future. Surely we will all be happier if we try to focus on the positive things in life rather than being stuck in the past or too worried about the future to develop as a person?

I agree with the quote Luis posted.  :)