This is hilarious. The visuals really help.

Hahah awesome!

I gotta say -- most people misuse the term "coincidence" when it comes to film. All you have to do is plant something early, and then pay it off later and it eliminates "coincidence." Coincidence in a constructed narrative medium, really has nothing to do with happenstance or chance, rather it has to do with that dues ex machina feeling -- that it was used as a simple escape mechanism. The real term should be convenience. For example, BACK TO THE FUTURE -- in real life, we would consider it quite a coincidence that within the same week 1) Doc Brown "invents" time travel 2) the lightning bolt hits the clock tower 3) The Enchantment Under the Sea dance occurs. (in fact, on the same day as the lightning strike, allowing both internal and external conflicts to culminate together). This all is coincidence. But it is coincidence that sets up the stakes of the movie. In other words, these are the "rules" of our world. Gotta get my parents together so they can kiss at The Enchantment Under the Sea dance, and gotta get the car to the clock tower precisely as lightning hits it. (And thank God, Doc was visiting himself when he first envisioned the flux capacitor, and not the time of the dinosaurs). It also sets up two ticking clocks. One would consider it to be coincidence that Jennifer writes her number on the back of the clock tower flyer, that later gives the solution of how they are going to get Marty back to the future -- a bolt of lightning. But this is not movie coincidence. What would actually be movie coincidence? If Marty simply spouted out some history about the lightning bolt and the clock tower when the problem of him getting back to the future arose. In terms of the character and his world -- this is actually likely he could have this knowledge. But it feels convenient. Too convenient. Whereas, an old guy giving him a flyer that details exactly when and where a lightning bolt hits, which he keeps because his girlfriend wrote her number on the back of it, is equally as coincidental (if not more so, let's be honest) -- BUT it doesn't feel "convenient." It is setup and planned. What is coincidence is if you AVOID these things. Craig Mazin points out that the irony is that not planting is actually what causes coincidence. The difference between good and bad "coincidence" is that, in the good example you let the audience put the pieces together, in the bad, you tell them, you do the work for them.