You need a lubricant. Lubricants such as, WD-40 will work just fine. Just stick the straw into the key hole and spray. Wipe off any excess that has seeped out of the hole. Lubricate your lock a few times a year. Why do you need to do this? Well your lock is made up of moving parts. It’s a mechanical device, these moving pieces will eventually take on some wear and begin to break down. Keeping them lubed will result in longer lasting lock.

Note: There are other things that could happen to your lock that would cause it to stop working. Obviously, lubing your locks will not protect it from everything.