It happens all the time! A stubborn zipper won’t cooperate by going up and down like it is meant to do. To remedy this, rub a bar of soap over the teeth of the zipper until you can see some soap residue on the zipper. Now pull up and down. The soap should have lubricated the zipper’s teeth to move easily. If you only use liquid soap (that may work too), try a candle, Vaseline, or lip balm. They should all give you the same result.