Slightly off topic but related, sometimes in the winter water gets in the lock and freezes. So the pins don't move and you break your key trying to turn the lock. Rain will do this but the most common cause is failing to tape over the lock when you spray clean the car/truck/tractor.
But the fix is easy:
Be sure you tape over the lock next time.
With a frozen lock, park the vehicle so the sun warms the lock.
After the lock has thawed (the key works) spray WD40 into the lock.
Anecdote - The passenger door lock on my truck has not worked for a month. The key goes in but won't turn. Yesterday in a mall I had trouble with the driver's lock too. I used the above procedure and everything is fine now.
Another thing, never ever buy aluminum keys. If you have one now, get it replaced and use the aluminum one as an emergency spare.