plot explanation - Why do the kicks have to occur simultaneously?

In Inception,
why do the kicks on the different levels have to occur simultaneously, rather than one
after another?

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class="normal">Answer

I love the
question.
Here's a summary from a very tight explanation (with some
drawings):

href="https://www.thisisbarry.com/film/inception-2010-movie-plot-ending-explained/"
rel="nofollow noreferrer">Inception and
Kicks

There were two types of dreams. The simple
construct with a mild sedative and the more complex construct with a strong sedative.

In the simple construct, one kick is enough. Kick can be
either to the self (eg: Arthur shot in the head) or a kick from
above (eg: Cobb dunked in bath tub). The sedative is light so there is no
synchronization required. In real life this can be equated to sleeping and dreaming
about falling, the fall in the dream wakes us up. Alternately someone wakes you up by
pushing you off the bed.

In a strong sedative, complex
construct dream - a single kick is not going to be enough. A person needs two
synchronized at the same instant. One kick to the self and one from the level above. The
synchronization is done using music. In the real world, this can be equated to being
under total anesthesia. Neither would a bad dream fall wake you up nor would pushing you
off the operating table. The reel part here is that if some how pushing you off the
table can be coincided with the fall in your dream, you can wake
up.

Now, in the act of inception on Fischer's mind, they
are in a complex heavily sedated dream. The only viable kick here is falling because
death will take you to limbo. As mentioned in another answer, waiting it out is not
going to work because weeks and months would need to pass in the lower layers. Waiting
it out is a possible option only in the first layer because there is limited time
dilation. Also a single kick from a level above or jumping off a cliff in the current
level wont work as a kick. The dreamer is far too sedated for that. A person needs to
fall in the current level and the level above simultaneously so so they plan. The
following kicks (falls) are planned:

Level 1 : Van
Falling
Level 2 : Falling by one floor (blowing up the floor) />Level 3 (inception level) : Falling from the building (blowing up the
structure)

Of course, things don't go as plan.
Hence they improvise on the kicks.
Here is the set of synchronized kicks that
each one receives per level of dream.
Point to note, no two people receive the
same two kick pairs.

Here's the image from the
link:
src="https://www.thisisbarry.com/wp-content/uploads/Inception/KickSequence.jpg"
alt="Kick Pairs">

So, other than dying in limbo,
everything else needs a pair of synchronized kicks. For more details, read the
link.