Grandma was waiting for the letter that she time vorpleled forward in time to herself. Just like the jet engine. The forces involved in the time-space warping that Don-don was already involved in after(before) the incidents in the film are what is actioning the seemingly illogical event streams. Apparently the message is that when you mix or alter your reality stream out of it's natural course, it can twist events long after and before into bizzare whorls and eddies of seemingly impossible synchronaistically connected events. Getting used to the fact that space-time is not actually linear. that all things and events actually happen at the 'same' time. and that our perception of time as linear and sequential is false. Gertting used to that in day to day life can be a daunting proposistion as mr. darko discovered. Our wee puny minds are just not sophisticated enough to get the concepts involved, except for the wee genius few, like don, And this movie is one of the few things I can think of that flawlwssly portrays this a-linearity. Lets name other things that a A-linear; My sentence structure. Good! moving on..The Frank character, is an amalgram of the entire event chain that has somehow gotten self-aware. Or perhaps a projection of donnie's vast mind. able to do his subconcious bidding forwards and backwards through time. Perhaps granny arranged to have letters sent to herself periodically, once she realized that she was going to be bat-shit-nutz in her later life. she figured out the reasons and the cure and set it up to be mailed to herself. Instructions on how to make yourself un-crazy. Invaluable eh? Frank was drunk when he hit the girlfriend right? drunkenness impairs memory. Where do you think all this memory goes? Maybe it collects in a big collage of missing drunken conciousness, malignantly doing random things in the psychosphere. heres another fun game, try to see if you can count the number of words that I have made up and used in this post..