A hypothetical question - if I get a key in the door lock from one side of the door, could I somehow use another key to open the door from the other side?
And what if you could "engineer" the stuck key - is it possible to allow the other key to open the door?
Before the key gets stuck, use graphite to lubricate the lock.
When the key gets stuck, there's nothing preventing you from using the other side of a lock (it's not the same keyhole).
If you can't gently unstick the key (forcefully removing a key may bend the pins in the lock, rendering it useless), then it's probably easiest to replace the entire lock. They aren't too expensive, and installing them where the same size lock already exists is a simple matter of unscrewing the old and screwing in the new.
This might not be the answer you are looking for but try to remove the lock from the door and take it to a locksmith. They can easily get the broken key out, with no damage to the lock. The price should not be very expensive, a lot cheaper than replacing with a good lock and if you need some keys remade, well you went to the right place.
If the key is all the way in the keyhole so that the pins are lined up, you can just use a screwdriver to turn the bolt.
You'd need a key extraction tool to remove it.
Assuming that I understand your question -- which as others have said is not well phrased -- Assuming this is a modern lockset rather than bit keys, a stuck key only blocks the cylinder it is stuck in. If there is a cylinder or thumbturn on the other side of the door, it would continue to operate the lock normally.
If that doesn't answer your question, please clarify.
(If by "engineer" you're trying to ask whether there's a way to make a key get stuck: Yes. This is sometimes done deliberately as a short-term solution to disable a lock until it can be rekeyed; there's also a version of this used to temporarily convert a keyed cylinder into a thumbturn. Details withheld; if you really want to know you can do the work to research or reinvent.7
