Sweden has a knife law, you can't carry knives in public without a valid reason.

In plenty of countries carrying knives in public is not allowed. You can own one for use in your home or work but don't brandish it out in the open.

The reason few people know this is because it's rarely ever needed, and the people violating that law are generally the people you want arrested anyway (e.g. because they're trying to stab someone).