David Crane, the creator of Pitfall, explains it all very nicely in a GDC Classic Game Postmortem [1]. I'm linking at the relevant timestamp, but the whole video is pure Atari 2600 goodness. The full Postmortems playlist is quite enjoyable too. I particularly liked the talks about the original Deus Ex, Myst, Loom, Adventure, Marble Madness, Ms. Pac-Man, Paperboy, Lemmings, and more. I find these videos very soothing and nostalgic. Got to rewatch them now...

[1]: https://youtu.be/tfAnxaWiSeE?list=PL2e4mYbwSTbbiX2uwspn0xiYb...