Are we trying to come up with a simple analogy that people can understand? Try this one-

tie 2 rubber bands to your keyring, one on each side of the ring
hold one rubber band in one hand
with the other hand pull upwards on the other rubber band, enough that the keys are picked up and the lower rubber band is stretched a little bit
now you have the keys suspended in the middle, one rubber band above stretched by your hand, one rubber band below stretched by your other hand
there is less tension in the bottom rubber band than the top rubber band, but there is tension in both rubber bands
the differences in the tensions is equal to the weight of the keys
that makes sense so far

now if you took a board and put 2 nails in it, the same distance apart as your hands were at the end of the above exercise
lay the board on a table, stretch the rubber bands and hook them onto the 2 nails
laying flat the 2 rubber bands should have the same tension and aren't affected by the keys because the keys are laying on the board
now turn the board so it is going up and down
you should have the keys suspended in the middle, one rubber band stretched above, one rubber band stretched below the keys
the keys are held up by BOTH rubber bands
rubber bands are not perfectly linearly elastic but lets assume they are for this discussion- the upper rubber band stretches a little bit more due to it picking up additional force equal to HALF of the weight of the keys, the lower rubber band relaxes a little bit due to its tension relieved by an amount equal to HALF of the weight of the keys, half plus half equals the weight of the keys and they are suspended in the middle as if by magic

And YES it would work if you stretched the keys between monofilament fishing line

(paraphrasing Mythbusters:
don't try to explain this at home, I'm a professional engineer, I do this for a living)