You can consider those ignition switch lock cylinders, door and trunk cylinders are all complicated devices. You should lubricate them with small amount of lubricant such as WD 40. The lubricant will help to prevent those tiny pins in the lock from binding.
When you can’t remove or insert the key, this means that the lock cylinder are jammed (from lack of lubricant) or are already broken. If you feel something is not right with the lock, lubricate the lock immediately. If this doesn’t solve the problem, replace the lock assembly.
On most of the cars, when you turn the ignition switch counter-clockwise to turn off the engine. If you force just a little harder counter-clockwise again, you might find another switch position. It is used to play radio without electrical current supplied to the ignition system. When the lock cylinders are already worn, the cylinders lose the resistance at the stop position. It will be easy for the key to slip past a certain position where it is unable to remove the key. If this happen, try turning the key slghtly clockwise while pulling the key. If still you can’t remove the key, just replace with a new ignition lock cylinder.
Another method is try to pull using a plier. Grasp the key with the plier and pull straight and be careful not to twist the key and break off the top. Try push in the key slightly and pull it out gently.
In order to prevent this problem from happening, remember to lubricate the cylinder and also don’t try to use the car key to open can lids or to cut the paper package. This is because car keys are mostly made of brass which is soft material and they are easy to break or bend.