A website called "Mystery Man on Film" has posted the transcript from the original 1978 story conference between Steven Spielberg, George Lucas, and Lawrence Kasdan where they hashed out the story for Raiders of the Lost Ark. It's an intriguing read, especially if you have an interest in how the story structure of a script like that comes about:

http://mysterymanonfilm.blogspot.com/2009/03/raiders-story-conference.html

Early on in the transcript, there's this exchange:

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Lucas-- Generally, the concept is a serial idea. Done like the
Republic serials. As a thirties serial. Which is where
a lot of stuff comes from anyway. One of the main ideas
was to have, depending on whether it would be every ten
minutes or every twenty minutes, a sort of a cliffhanger
situation that we get our hero into. If it's every ten
minutes we do it twelve times. I think that may be a
little much. Six times is plenty.

Speilberg — And each cliffhanger is better than the one before.

Lucas — That is the progression we have to do. It's hard
to come up with. The trouble with cliff hangers is, you
get somebody into something, you sort have to get them
out in a plausible way. A believable way, anyway.
That's another JLmportant concept of the movie — that it
be totally believable. It's a spaghetti western, only
it takes place in the thirties. Or it's James Bond and
it takes place in the thirties. Except James Bond tends
to get a little outrageous at times. We're going to take
the.unrealistic side of it off. and make it more like the
Clint Eastwood westerns.

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I can't help reading that and noting that, 30 years later, Indiana Jones escapes an atomic blast in a refrigerator. How times change.