[_jal]

Downloads can occupy some fuzzy middle ground between unknown and deterministic.

The normal case is that bandwidth throughput can be estimated well enough to make humans happy. But a broken network throws that out the window and will do its best to find ways to make your progress bar behave weirdly.

I can't remember what it was, but there was a Mac app a very long time ago (System 7 era, in the 90s) - maybe a news reader? - that would eventually hide the progress bar and show a message about bad networking when that happened.