Soap Wheel

Most soaps fall under two categories, Loads and Loads of Characters and Long Runners.

Over this long period they have perfected the method of keeping the stories moving and the characters changing: The A B C plot wheel.

Plot A -- one of the teenagers is pregnant. Halfway through this Story Arc, Plot B will kick in - someone has amnesia. By the time Plot A is finished and the teenager has undergone a heartwarming transformation, the main character in Plot B is in a hospital bed and has just remembered that his wife was the one who tried to kill him. Then in another part of the cast, a long-running character's never-before-seen daughter has started taking drugs - Plot C starts. When their parents find out, Plot B's wife is in jail and he is happily settled in his new life. Meanwhile Plot A's baby is now a toddler due to Soap Opera Rapid Aging Syndrome, and is being stalked by her real father and the mother is going slowly mad.

By starting a new story about half way through another, there is a constant rotation of new plots. The drama keeps flowing, and these people never receive a moment's rest. This is the Soap Wheel, the time-tested way to turn Loads and Loads of Characters into a nonstop cavalcade of drama.

For a similar trope that happens in a single episode of a series, see Two Lines, No Waiting. For the "episodic" version of this trope, see Four Lines, All Waiting.

Anime and Manga

 * Happens in the Kyoto Animation version of Kanon, too.

Comic Books

 * Superhero comic books that have strong supporting casts often do this as well. Though the practice dwindled once Writing for the Trade became popular, it has been making a comeback lately.
 * For example, see the early issues of John Byrne's run on West Coast Avengers. During the "Vision Disassembled" arc hints are dropped about the Great Lakes Avengers. When the GLA take the main stage, you start seeing subplots about the Scarlet Witch's potential abduction. During all of this, the Witch's "imaginary children" plotline is given a few panels each issue.

Live-Action TV

 * Eastenders was an early pioneer of this format and still uses it today.
 * Coronation Street: Another long running British soap.
 * Hollyoaks
 * Family Affairs
 * Neighbours
 * Home and Away
 * Days of Our Lives
 * Dynasty
 * Almost every other show on the Soap Opera index.
 * Babylon 5 - Word of God is that each season is structured to introduce a new Plot Arc in the first several episodes, while resolving the Plot Arc of the previous season about on third of the way in.
 * J. Michael Straczynski, the series creator, stated that he felt the biggest weakness of most "mystery driven" series is that at some point viewers will either get bored with the mystery or decide that it will never end up being solved. By actually resolving previous arcs viewers are more invested in the current one.
 * And let's not forget Soap!
 * Battlestar Galactica used this. In the Universe Bible, Ron Moore cited Hill Street Blues as an influence.

Music

 * Done musically by Dream Theater. The fourth through eight albums were composed in a way that turned them into one continuous album if listened from start to finish, but in the second album of the series, they introduced a multi-part song that would not be finished until the tenth album.

Professional Wrestling

 * Professional Wrestling uses this on a regular basis, rotating feuds in the undercard—which fits, as it's often referred to as a Soap Opera for men.

Tabletop Games

 * Some Game Masters who run Tabletop Roleplaying Games use this technique to keep their campaigns open-ended, planting hooks for future adventures in the current one.

Web Comics

 * Rumors of War makes use of a variant of the Soap Wheel (by combining Rotating Protagonists with Time Skips) to create a Cast-Go-Round. The plot keeps the moving even though tons of significant action takes place off-screen. Even the characters are left but to comment on what's happened and prepare for the next.