The original Rocky is of course a very good, and mostly very quiet film, with famous moments of noise: boxing matches and yelling bouts and times when Bill Conti's score lets itself get loud. One time this happens is Rocky's dawn run through Philadelphia. Once I watched the DVD documentary on Rocky and noted how a lot of that was shot with just Sylvester Stallone, director John G. Avildson and the camera operator driving along in a van until they got to an interesting place to film, where Stallone would jump out and run and run and run, the van driving alongside and the camera poking out. Often in the final film, that running footage would be cut right before Stallone stopped running on that particular take.
Stallone mentioned how hard it could be to motivate himself to the necessary exertion on those runs. The not-so-obvious thought? He couldn't motivate himself with Bill Conti's famous theme from Rocky: it hadn't been written yet.
That strikes me every once in a while: realizing how a creative work didn't exist at one point, so we didn't yet have it as a reference. How many of us hum "Gonna Fly Now" when we're trying to get motivated? (And now I wonder if it was easier for Stallone to motivate himself to exertion for the training montages in Rockys Two through Six because "Gonna Fly Now" already was around...)
Not the deepest thought I've had, but why not share it?