There are many different ways one can view bitAssets, and different analogies to draw. Some people may find this a useful analogy in the context of "the future of banking". I'd be interested to know if others find this useful, or in what way it could risk being misleading or inaccurate.
> start analogy
The collateral pools for each bitAsset can be thought of as separate vaults
A bitAsset is a key
that allows the holder to go to the vault, unlock it, and receive BTS to the value of a unit of the bitAsset. So for example, a bitUSD, or a key to the USD vault, allows you to unlock $1 worth of BTS from the vault, at which point that key is destroyed. A bitBTC, or a key to the BTC vault, allows you to unlock 1 BTC worth of BTS from the vault, at which point that key is destroyed.
You don't have immediate access to the vault however, and need to wait in a queue for a maximum of 30 days. People who choose to not demand their full entitlement are first in the queue, while those demanding their full entitlement are at the back and need to wait longest. In the meantime, if you wish to sell your key more urgently, you can do that. You will probably need to accept a discount, but hopefully not too deep a discount because people will be prepared to pay for a key that can access the contents of the vault within 30 days.
[Edit: I would probably add something about the keys being able to be traded in a free market and used in transactions]
> end analogy
That's the analogy, now let me explain how it works.
Whenever there is demand for a key (bitAsset) in excess of the supply (keys already available), the price for a key will push to a premium (price moves over the peg). This will encourage a key-maker (in reality a spread-trader) to create a new key. The way he technically does this is as follows. He creates the key by taking a simultaneous long bitAsset position and short bitAsset position, in the process placing 3x the value of the bitAsset in the form of BTS into the vault (collateral pool). Then he takes his key (the long bitAsset position) and sells it on the market at a premium to meet the demand.
Now there are several ways the key-maker can get his BTS back. At the end of 30 days, the vault automatically opens to the first key-bearer in the queue (the short position is closed against the bitAsset seller with lowest ask). The key-bearer receives the entitlement of BTS that they demanded with their key, the remaining vault contents placed by the key-maker go to him, and the key is automatically destroyed (the supply of bitAsset reduces because a long and short have been destroyed). The key-maker may also go to the market anytime within the 30 days and buy the key cheaper if they can (buy back a long position in the bitAsset), thus if they desire unlocking the contents of the vault for themselves (sell the bitAsset into the cover of their short position). If keys get too cheap, the key-maker is actually incentivised to open the vaults, take out the collateral and destroy the keys (i.e. reducing bitAsset supply).
Note that it has been shown in another thread that any key-bearer lined up in the vault queue awaiting their full entitlement (i.e. sitting with a bitAsset sell order at the feed price) can, in theory, be guaranteed to receive that within 30 days. See https://bitsharestalk.org/index.php?topic=9861.msg128211#msg128211
In practice this can be difficult however, because it (currently) requires manually moving one's order with the feed price, which in turn has a cost attached, and may also mean it takes longer than 30 days to achieve the sale price at the peg.